Code cleanup for executive

This pull request just does some code clean up to ProtoCore.DSASM.Executive based on resharper's code analysis result. It includes:
  * Remove redundant ``return`` at the end of ``void`` function
  * Remove redundant namespace qualifiers, for example, ``ProtoCore.DSASM.``
  * Remove dead codes which include some functions and variables that are declared but never used.
  * Remove redundant value initialization if the variable will get assigned later on.

@junmendoza , please review the change. Thanks.