x86/mm: Remove reset_lazy_tlbstate()

The only call site also calls idle_task_exit(), and idle_task_exit()
puts us into a clean state by explicitly switching to init_mm.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/3acc7ad02a2ec060d2321a1e0f6de1cb90069517.1498022414.git.luto@kernel.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>