Enable checkstyle rule for boolean return statement
that can be simplified.

Enable the "SimplifyBooleanReturn" checkstyle rule and fix
the violations is causes.

Change-Id: I3465c76d863d49ca71895d9c8d55b86e4a37d0f1
diff --git a/conf/checkstyle/sun_checks.xml b/conf/checkstyle/sun_checks.xml
index 5baa022..db7e909 100644
--- a/conf/checkstyle/sun_checks.xml
+++ b/conf/checkstyle/sun_checks.xml
@@ -223,10 +223,7 @@
           <property name="severity" value="warning"/>
         </module>
 
-        <module name="SimplifyBooleanReturn">
-          <property name="severity" value="warning"/>
-        </module>
-
+        <module name="SimplifyBooleanReturn"/>
 
         <!-- Checks for class design                         -->
         <!-- See http://checkstyle.sf.net/config_design.html -->