Remove SK_SUPPORT_LEGACY_DEEPFLATTENING.

This was needed for pictures before v33, and we're now requiring v35+.

Will follow up with the same for skia/ext/pixel_ref_utils_unittest.cc

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/52c293547b973f7fb5de3c83f5062b07d759ab88

Review URL: https://codereview.chromium.org/769953002
115 files changed