Remove last SK_SUPPORT_LEGACY_SHADER_LOCALMATRIX.

Should have been included in https://codereview.chromium.org/379323002
but it was overlooked. As of that CL, the flag does not do anything.

BUG=skia:1976
R=reed@google.com

Author: scroggo@google.com

Review URL: https://codereview.chromium.org/390033002

gyp/common_conditions.gypi

@@ -374,7 +374,6 @@
         'SK_MUTEX_PLATFORM_H "../../src/ports/SkMutex_pthread.h"',
         # Transitional, for deprecated SkCanvas::SaveFlags methods.
         'SK_ATTR_DEPRECATED=SK_NOTHING_ARG1',
-        'SK_SUPPORT_LEGACY_SHADER_LOCALMATRIX',
         'SK_DEFAULT_GLOBAL_DISCARDABLE_MEMORY_POOL_SIZE (512 * 1024)',
         'SK_IGNORE_ETC1_SUPPORT',
         # Defines from skia_for_android_framework_defines.gypi