Removed unused versions md5 code

It looks like md5 was used previously to identify the most recent file
in the versions list, which seem to be old code, as now the versions
list doesn't contain the current file any more.

This fix removes the md5 code which caused performance issues with big
files.
Merge pull request #7227 from owncloud/stable5-removeunusedversionsmd5

Removed unused versions md5 code