mm/kasan: Remove the ULONG_MAX stack trace hackery

No architecture terminates the stack trace with ULONG_MAX anymore. Remove
the cruft.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: kasan-dev@googlegroups.com
Cc: linux-mm@kvack.org
Link: https://lkml.kernel.org/r/20190410103644.750219625@linutronix.de

mm/kasan/common.c

@@ -74,9 +74,6 @@ static inline depot_stack_handle_t save_stack(gfp_t flags)
 
 	save_stack_trace(&trace);
 	filter_irq_stacks(&trace);
-	if (trace.nr_entries != 0 &&
-	    trace.entries[trace.nr_entries-1] == ULONG_MAX)
-		trace.nr_entries--;
 
 	return depot_save_stack(&trace, flags);
 }