ReqMgr - Processing, Production dead code clean-up

Entire two packages

WMCore/RequestManager/RequestMaker/Processing
WMCore/RequestManager/RequestMaker/Production

were unused, and just one class referenced from the unittests,
and even that was in vain.

Removing all files, tested on VM with reqmgr.py
Fixes #4420
Merge pull request #4421 from zdenekmaxa/reqmgr-dead-processing-production-code-cleanup

ReqMgr - Processing, Production dead code clean-up