gtm: reenable deprecation warnings

The roll to gtm 51863009 fixed these.

Bug: 386671
Change-Id: I868b7bb711dd3871af7b9d5f812dcf66c5db1439
Reviewed-on: https://chromium-review.googlesource.com/c/1482556
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Auto-Submit: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634663}

third_party/google_toolbox_for_mac/BUILD.gn

@@ -39,11 +39,6 @@ component("google_toolbox_for_mac") {
       "Cocoa.framework",
       "QuartzCore.framework",
     ]
-
-    # TODO(crbug.com/841631): GTM uses accessibility APIs that are deprecated as
-    # of 10.10. These can't yet be compiled out, so for now, ignore deprecated
-    # declarations in GTM altogether.
-    cflags = [ "-Wno-deprecated-declarations" ]
   } else {  # is_ios
     sources += [
       "src/DebugUtils/GTMMethodCheck.h",