kallsyms: remove deprecated print_fn_descriptor_symbol()

According to feature-removal-schedule.txt, it is the time to remove
print_fn_descriptor_symbol().

And a quick grep shows that it no longer has any callers.

Signed-off-by: WANG Cong <amwang@redhat.com>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>