Enable PMD rule SimplifyBooleanReturns and fix violations

brouter-util/src/main/java/btools/util/CompactLongSet.java

@@ -141,10 +141,7 @@ public class CompactLongSet {
         n = nn;
       }
     }
-    if (a[n] == id) {
-      return true;
-    }
-    return false;
+    return a[n] == id;
   }
 
   protected void moveToFrozenArray(long[] faid) {

brouter-util/src/main/java/btools/util/FrozenLongSet.java

@@ -61,10 +61,7 @@ public class FrozenLongSet extends CompactLongSet {
       }
       offset >>= 1;
     }
-    if (a[n] == id) {
-      return true;
-    }
-    return false;
+    return a[n] == id;
   }
 
 }

config/pmd/pmd-ruleset.xml

@@ -31,7 +31,6 @@
         <exclude name="PreserveStackTrace" />
         <exclude name="PrimitiveWrapperInstantiation" />
         <exclude name="ReturnEmptyCollectionRatherThanNull" />
-        <exclude name="SimplifyBooleanReturns" />
         <exclude name="UncommentedEmptyConstructor" />
         <exclude name="UncommentedEmptyMethodBody" />
         <exclude name="UnusedFormalParameter" />