afs: cleanup remnant afs_vfs_mount prototype in afs_call.c

afs: cleanup remnant afs_vfs_mount prototype in afs_call.c

The call to afs_vfs_mount() in afs_call.c was removed in commit
a5ab24af71efe6b80eb0f78d1979c5ab1d1e594d.  Remove the remnant prototype
and the useless conditionals around it.

Reviewed-on: https://gerrit.openafs.org/12275
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 91f5cecc937923e16c5feda675fccd36d2b95164)

Change-Id: I6463d012c0c00b4a2738fa1045e822cda5c3304a
Reviewed-on: https://gerrit.openafs.org/12305
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>