Figure out logging_file table #106

Another from #102. There is a logging_file table which I think is completely unused. It looks like maybe the idea was to support having the processing codes hook in to the dbprocessing logging setup, but that never happened. So I think all that needs to happen is removal...I'll have to do a little digging in the codebase to be sure.

This is a pretty old table; it existed in the 2010-10-04 schema, which predates the existence of the inspector table (!)

OS, Python version, and dependency version information:

Linux-4.15.0-163-generic-x86_64-with-Ubuntu-18.04-bionic
sys.version_info(major=2, minor=7, micro=17, releaselevel='final', serial=0)
sqlalchemy=1.1.11

Version of dbprocessing

#102 , i.e. 1d5a938 or jtniehof/dbprocessing:document_tables

Closure condition

This issue should be closed when a commit is merged with migration support for deleting this table.