Virtual functions are removed from TSymbol, so the warning for
non-virtual destructor found in a class with virtual functions can be
enabled.

BUG=angleproject:2417
TEST=angle_unittests

Change-Id: Icd0ea2c77ce826739fbe954137f8ee78e6ef5386
Reviewed-on: https://chromium-review.googlesource.com/1051830
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>