Return to suppressing deprecation warnings

The previous change re-enabled warnings too aggressively. While the icu
target built correctly the icu nacl targets (such as
irt_x64/obj/third_party/icu/icuuc/uidna.o on Windows and
newlib_pnacl/obj/third_party/icu/icuuc/uidna.o on other platforms)
failed to compile due to deprecation warnings. This change adds back
suppression of that one warning.

BUG=21515
R=thakis@chromium.org

Review URL: https://codereview.chromium.org/2504463002 .
1 file changed