9p: remove deprecated v9fs_fid_lookup_remove()

This patch removes the v9fs_fid_lookup_remove which is no longer used.

Based on original patch from Adrian Bunk <bunk@stusta.de> which
used #if 0 to isolate the code.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>