signals: rename rm_from_queue_full() to flush_sigqueue_mask()

signals: rename rm_from_queue_full() to flush_sigqueue_mask()

"rm_from_queue_full" looks ugly and misleading, especially now that
rm_from_queue() has gone away.  Rename it to flush_sigqueue_mask(), this
matches flush_sigqueue() we already have.

Also remove the obsolete comment which explains the difference with
rm_from_queue() we already killed.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>