Remove SkAutoSTMalloc windows hack

Now that SkAutoSTMalloc is supported on windows remove the hack from
GlyphPageTreeNodeSkia.

R=pdr@chromium.org
BUG=

Review URL: https://codereview.chromium.org/56213003

git-svn-id: svn://svn.chromium.org/blink/trunk@161346 bbb929c8-8fbe-4397-9dbb-9b2b20218538