Remove SK_SUPPORT_LEGACY_GET_PIXELS_ENUM.

SK_SUPPORT_LEGACY_GET_PIXELS_ENUM just set a \#define to convert
onGetPixelsEnum
to
onGetPixels

Now that Chrome has been updated to override onGetPixels, there is no
need for the define.

BUG=skia:3257

Review URL: https://codereview.chromium.org/933853004
2 files changed