Make SkGr.h private and remove unused functions

BUG=skia:

Change-Id: I6699d00c5412ed9d9bf14b032a08b06b1c766bce
Reviewed-on: https://skia-review.googlesource.com/9398
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/gn/gpu.gni b/gn/gpu.gni
index 4cab21f..e34ff45 100644
--- a/gn/gpu.gni
+++ b/gn/gpu.gni
@@ -453,13 +453,11 @@
   "$_src/gpu/glsl/GrGLSLXferProcessor.h",
 
   # Sk files
-  "$_include/gpu/SkGr.h",
-
   "$_src/gpu/SkGpuDevice.cpp",
   "$_src/gpu/SkGpuDevice.h",
   "$_src/gpu/SkGpuDevice_drawTexture.cpp",
+  "$_src/gpu/SkGr.h",
   "$_src/gpu/SkGr.cpp",
-  "$_src/gpu/SkGrPriv.h",
 
   "$_src/image/SkImage_Gpu.h",
   "$_src/image/SkImage_Gpu.cpp",