freezer: remove unused @sig_only from freeze_task()

After "freezer: make freezing() test freeze conditions in effect
instead of TIF_FREEZE", freezing() returns authoritative answer on
whether the current task should freeze or not and freeze_task()
doesn't need or use @sig_only.  Remove it.

While at it, rewrite function comment for freeze_task() and rename
@sig_only to @user_only in try_to_freeze_tasks().

This patch doesn't cause any functional change.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>
diff --git a/include/linux/freezer.h b/include/linux/freezer.h
index a0f1b3a..a28842e 100644
--- a/include/linux/freezer.h
+++ b/include/linux/freezer.h
@@ -48,7 +48,7 @@
 	return __refrigerator(false);
 }
 
-extern bool freeze_task(struct task_struct *p, bool sig_only);
+extern bool freeze_task(struct task_struct *p);
 extern bool __set_freezable(bool with_signal);
 
 #ifdef CONFIG_CGROUP_FREEZER