remove code behind SK_SUPPORT_LEGACY_PROCXFERMODE

BUG=skia:
R=scroggo@google.com

Review URL: https://codereview.chromium.org/264923004

git-svn-id: http://skia.googlecode.com/svn/trunk@14504 2bbb7eff-a529-9590-31e7-b0007b416f81
4 files changed