afs: Fix incorrect triggering of sillyrename on 3rd-party invalidation

The AFS filesystem is currently triggering the silly-rename cleanup from
afs_d_revalidate() when it sees that a dentry has been changed by a third
party[1].  It should not be doing this as the cleanup includes deleting the
silly-rename target file on iput.

Fix this by removing the places in the d_revalidate handling that validate
anything other than the directory and the dirent.  It probably should not
be looking to validate the target inode of the dentry also.

This includes removing the point in afs_d_revalidate() where the inode that
a dentry used to point to was marked as being deleted (AFS_VNODE_DELETED).
We don't know it got deleted.  It could have been renamed or it could have
hard links remaining.

This was reproduced by cloning a git repo onto an afs volume on one
machine, switching to another machine and doing "git status", then
switching back to the first and doing "git status".  The second status
would show weird output due to ".git/index" getting deleted by the above
mentioned mechanism.

A simpler way to do it is to do:

	machine 1: touch a
	machine 2: touch b; mv -f b a
	machine 1: stat a

on an afs volume.  The bug shows up as the stat failing with ENOENT and the
file server log showing that machine 1 deleted "a".

Fixes: 79ddbfa5 ("afs: Implement sillyrename for unlink and rename")
Reported-by: Markus Suvanto <markus.suvanto@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Markus Suvanto <markus.suvanto@gmail.com>
cc: linux-afs@lists.infradead.org
Link: https://bugzilla.kernel.org/show_bug.cgi?id=214217#c4 [1]
Link: https://lore.kernel.org/r/163111668100.283156.3851669884664475428.stgit@warthog.procyon.org.uk/