Remove unnecessary pointer increment

These variables are about to go out of scope anyway, and will be
re-declared with the proper value on the next iteration of the loop.

Change-Id: I2d3cfa1c888057b98125c83854f6af817225d0b3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/309958
Commit-Queue: Leon Scroggins <scroggo@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
Auto-Submit: Leon Scroggins <scroggo@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>

tools/ToolUtils.cpp

@@ -439,8 +439,6 @@ bool equal_pixels(const SkPixmap& a, const SkPixmap& b) {
         if (memcmp(aptr, bptr, a.width() * a.info().bytesPerPixel())) {
             return false;
         }
-        aptr += a.rowBytes();
-        bptr += b.rowBytes();
     }
     return true;
 }