Remove redundant return statements in Scala code to get better consistency

In Scala return keyword is not needed at the end of method because Scala always return something.
This PR is to remove simple redundant return keyword in the Scala code:
-) At the end of method returning a variable
-) Modify some simple if-else code to remove return word for checking special cases.
-) Ignore some of the return keywird used in long if-else code and loops and synchronized code.