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/tests/SpecialImageTest.cpp b/tests/SpecialImageTest.cpp
index c033ebc..f9a0147 100644
--- a/tests/SpecialImageTest.cpp
+++ b/tests/SpecialImageTest.cpp
@@ -18,7 +18,7 @@
 #if SK_SUPPORT_GPU
 #include "GrContext.h"
 #include "GrSurfaceProxy.h"
-#include "SkGrPriv.h"
+#include "SkGr.h"
 #endif