Remove a method almost duplicated in other method

Change-Id: Idc9bd0cb53696f379fe77b7b30683eb977a597ad
diff --git a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/DiscreteResources.java b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/DiscreteResources.java
index 6c65122..b6acccc 100644
--- a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/DiscreteResources.java
+++ b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/DiscreteResources.java
@@ -86,15 +86,6 @@
     DiscreteResources add(DiscreteResources other);
 
     /**
-     * Returns a difference set of this instance and the given resources.
-     * Note: This method returns a new instance, not mutate the current intance.
-     *
-     * @param removed resources
-     * @return a new DiscreteResources instance representing a difference set
-     */
-    DiscreteResources remove(Set<DiscreteResource> removed);
-
-    /**
      * Returns all of resources this instance holds.
      *
      * @return all resources
diff --git a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/EmptyDiscreteResources.java b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/EmptyDiscreteResources.java
index 9211576..d7c0f24 100644
--- a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/EmptyDiscreteResources.java
+++ b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/EmptyDiscreteResources.java
@@ -58,11 +58,6 @@
     }
 
     @Override
-    public DiscreteResources remove(Set<DiscreteResource> removed) {
-        return this;
-    }
-
-    @Override
     public Set<DiscreteResource> values() {
         return ImmutableSet.of();
     }
diff --git a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/EncodableDiscreteResources.java b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/EncodableDiscreteResources.java
index 99352ac..25ec5a7 100644
--- a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/EncodableDiscreteResources.java
+++ b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/EncodableDiscreteResources.java
@@ -108,11 +108,6 @@
     }
 
     @Override
-    public DiscreteResources remove(Set<DiscreteResource> removed) {
-        return of(parent, Sets.difference(values(), removed));
-    }
-
-    @Override
     public Set<DiscreteResource> values() {
         return values.values().stream()
                 .flatMap(x -> x.values(parent.id()).stream())
diff --git a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/GenericDiscreteResources.java b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/GenericDiscreteResources.java
index d35a477..79eb13d 100644
--- a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/GenericDiscreteResources.java
+++ b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/GenericDiscreteResources.java
@@ -79,12 +79,6 @@
         return new GenericDiscreteResources(newValues);
     }
 
-    // returns a new instance, not mutate the current instance
-    @Override
-    public DiscreteResources remove(Set<DiscreteResource> removed) {
-        return of(Sets.difference(this.values, removed));
-    }
-
     @Override
     public Set<DiscreteResource> values() {
         // breaks immutability, but intentionally returns the field
diff --git a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/TransactionalDiscreteResourceSubStore.java b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/TransactionalDiscreteResourceSubStore.java
index d2cecb0..1f51f7b 100644
--- a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/TransactionalDiscreteResourceSubStore.java
+++ b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/TransactionalDiscreteResourceSubStore.java
@@ -102,7 +102,8 @@
             return true;
         }
 
-        DiscreteResources newValues = oldValues.remove(values);
+        DiscreteResources requested = DiscreteResources.of(values);
+        DiscreteResources newValues = oldValues.difference(requested);
         return childMap.replace(key, oldValues, newValues);
     }
 
diff --git a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/UnifiedDiscreteResources.java b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/UnifiedDiscreteResources.java
index 1959a59..0bd1fca 100644
--- a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/UnifiedDiscreteResources.java
+++ b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/UnifiedDiscreteResources.java
@@ -88,11 +88,6 @@
     }
 
     @Override
-    public DiscreteResources remove(Set<DiscreteResource> removed) {
-        return of(Sets.difference(values(), removed));
-    }
-
-    @Override
     public Set<DiscreteResource> values() {
         return Stream.concat(encodables.values().stream(), generics.values().stream())
                 .collect(Collectors.toCollection(LinkedHashSet::new));