proc: do translation + unlink atomically at remove_proc_entry()

remove_proc_entry() does

	lock
	lookup parent
	unlock
	lock
	unlink proc entry from lists
	unlock

which can be made bit more correct by doing parent translation + unlink
without dropping lock.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>