inherit maven-javadoc-version from parent pom

Change-Id: I2ee617830985d7f7193363c7977ff67ade5cbca8
diff --git a/docs/external.xml b/docs/external.xml
index 37463c3..d004527 100644
--- a/docs/external.xml
+++ b/docs/external.xml
@@ -46,7 +46,6 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-javadoc-plugin</artifactId>
-                <version>2.10.3</version>
                 <configuration>
                     <show>package</show>
                     <excludePackageNames>@external-excludes</excludePackageNames>
diff --git a/docs/internal.xml b/docs/internal.xml
index d1525aa..f06ca13 100644
--- a/docs/internal.xml
+++ b/docs/internal.xml
@@ -46,7 +46,6 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-javadoc-plugin</artifactId>
-                <version>2.10.3</version>
                 <configuration>
                     <show>package</show>
                     <docfilessubdirs>true</docfilessubdirs>
diff --git a/tools/build/pom.xml b/tools/build/pom.xml
index ea473ed..33b3a09 100644
--- a/tools/build/pom.xml
+++ b/tools/build/pom.xml
@@ -81,7 +81,6 @@
                     <plugin>
                         <groupId>org.apache.maven.plugins</groupId>
                         <artifactId>maven-javadoc-plugin</artifactId>
-                        <version>2.9.1</version>
                         <executions>
                             <execution>
                                 <id>attach-javadocs</id>