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/GrTexture.cpp b/src/gpu/GrTexture.cpp
index 20cd597..4f95730 100644
--- a/src/gpu/GrTexture.cpp
+++ b/src/gpu/GrTexture.cpp
@@ -172,7 +172,7 @@
     GrResourceKey::ResourceFlags flags = 0;
     bool tiled = NULL != params && params->isTiled();
     if (tiled && !gpu->caps()->npotTextureTileSupport()) {
-        if (!GrIsPow2(desc.fWidth) || !GrIsPow2(desc.fHeight)) {
+        if (!SkIsPow2(desc.fWidth) || !SkIsPow2(desc.fHeight)) {
             flags |= kStretchToPOT_TextureFlag;
             switch(params->filterMode()) {
                 case GrTextureParams::kNone_FilterMode: