Revert "Vary twemproxy config location based on getRealmSpecificFilename()"

/usr/local/lib/mw-deployment-vars.sh is not valid dash syntax and as a
result upstart fails badly to start the job.

This reverts commit 70fed5288d2697aa3eead6af1932a4c4d89dc70c.

Change-Id: I587d8af7871e8db695171a5296562e33f9ccb128