Remove unnecessary getColorSpace() API from SkCodec

Not needed since now we can get it from the SkImageInfo.

TBR=reed@google.com
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2170793004

Review-Url: https://codereview.chromium.org/2170793004
8 files changed