remove unused GM flags

gm/peekpixels.cpp

Index: gm/peekpixels.cpp
diff --git a/gm/peekpixels.cpp b/gm/peekpixels.cpp
index 24e509c42b64f3d963b27459af5e59ddebf4eb80..3a881ff8c560823c9e13245e2e1b97d0c269d3d1 100644
--- a/gm/peekpixels.cpp
+++ b/gm/peekpixels.cpp
@@ -64,12 +64,6 @@ protected:
         }
     }
 
-    uint32_t onGetFlags() const SK_OVERRIDE {
-        // we explicitly test peekPixels and readPixels, neither of which
-        // return something for a picture-backed canvas, so we skip that test.
-        return kSkipPicture_Flag;
-    }
-
 private:
     typedef skiagm::GM INHERITED;
 };