Remove GrIsPow2 in favor of SkIsPow2.

Looks like there is no good reason to have two copies of this function
doing the same thing with different name.

BUG=None
TEST=make tests
R=bsalomon@google.com

Author: tfarina@chromium.org

Review URL: https://codereview.chromium.org/318873002
diff --git a/src/gpu/GrGpu.cpp b/src/gpu/GrGpu.cpp
index 36a9cf1..fd249de 100644
--- a/src/gpu/GrGpu.cpp
+++ b/src/gpu/GrGpu.cpp
@@ -125,10 +125,10 @@
         SkASSERT((desc.fFlags & kRenderTarget_GrTextureFlagBit) == 0);
 
         if (!this->caps()->npotTextureTileSupport() &&
-            (!GrIsPow2(desc.fWidth) || !GrIsPow2(desc.fHeight))) {
+            (!SkIsPow2(desc.fWidth) || !SkIsPow2(desc.fHeight))) {
             return NULL;
         }
-        
+
         this->handleDirtyContext();
         tex = this->onCreateCompressedTexture(desc, srcData);
     } else {