Remove SkLinearGradient::kForce4fContext_PrivateFlag

... and related tests/gms.

We now exercise the 4f impl with raster-pipeline/burst, no need for a
special test flag.

Change-Id: If67684d2d8840b3c413db9eeebb051f59cbc5a34
Reviewed-on: https://skia-review.googlesource.com/19025
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
diff --git a/src/shaders/gradients/SkLinearGradient.cpp b/src/shaders/gradients/SkLinearGradient.cpp
index 2bce02e..f803d5e 100644
--- a/src/shaders/gradients/SkLinearGradient.cpp
+++ b/src/shaders/gradients/SkLinearGradient.cpp
@@ -43,8 +43,7 @@
 #ifdef FORCE_4F_CONTEXT
     return true;
 #else
-    return rec.fPreferredDstType == SkShaderBase::ContextRec::kPM4f_DstType
-        || SkToBool(flags & SkLinearGradient::kForce4fContext_PrivateFlag);
+    return rec.fPreferredDstType == SkShaderBase::ContextRec::kPM4f_DstType;
 #endif
 }