Removed unused Subversion().unpack in unpack_file
Removed unused Subversion().unpack in unpack_file

`download.unpack_url` already calls `unpack_vcs_link`, it looks like
this was leftover from before that change.

rouge8/pip,xavfernandez/pip,pradyunsg/pip,pypa/pip,pradyunsg/pip,rouge8/pip,xavfernandez/pip,pfmoore/pip,pfmoore/pip,sbidoul/pip,rouge8/pip,sbidoul/pip,xavfernandez/pip,pypa/pip