Remove SkImageInfoIsGammaCorrect, etc...

Our internal definition is (and will continue to be) that anything with
a color space is gamma correct. F16 is irrelevant (whether or not we
choose to support untagged F16). This makes these helpers less than
helpful, and lets us remove them from (public) API.

API change is just removal (of unused functions).

TBR=reed@google.com

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4228

Change-Id: Ia84a423548bfee14a3ba4a43d6d5b8c4686fb5ff
Reviewed-on: https://skia-review.googlesource.com/4228
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
diff --git a/samplecode/SampleApp.cpp b/samplecode/SampleApp.cpp
index 6f0e958..6722429 100644
--- a/samplecode/SampleApp.cpp
+++ b/samplecode/SampleApp.cpp
@@ -350,7 +350,7 @@
             // With ten-bit output, we need to manually apply the gamma of the output device
             // (unless we're in non-gamma correct mode, in which case our data is already
             // fake-sRGB, like we're expected to put in the 10-bit buffer):
-            bool doGamma = (fActualColorBits == 30) && SkImageInfoIsGammaCorrect(win->info());
+            bool doGamma = (fActualColorBits == 30) && win->info().colorSpace();
 
             SkPaint gammaPaint;
             gammaPaint.setBlendMode(SkBlendMode::kSrc);