Remove unused encoding parameter in RequestDBWriter.py

[oljemark]

Impact of the bug
WMCore/Services/RequestDB: The internal variable _propertyNeedToBeEncoded (defined here https://github.com/dmwm/WMCore/blob/master/src/python/WMCore/Services/RequestDB/RequestDBWriter.py#L10 ) is not used anywhere else, and could be removed?

Describe the bug
This variable was used to enumerate (allowed?) keywords that were JSON-encoded instead of saved raw, but the variable stopped being referred to already two weeks later in 2014, in a commit in PR #5550 (commit c21fcb8) , and the choice to encode or not was removed in PR #6006 ,so I'm not sure if adding keyword PriorityTransition to this variable did anything at all in PR #8679 ?

How to reproduce it

Expected behavior
Remove if not used, or in case this whole file is unused?

Additional context and error message