C API: remove dead code, simplify boilerplate

gm/cgms.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gm.h"
 #include "sk_types.h"
 
 extern "C" void sk_test_c_api(sk_canvas_t*);
 
-class C_GM : public skiagm::GM {
-public:
-    C_GM() {}
-
-protected:
-    SkString onShortName() override {
-        return SkString("c_gms");
-    }
-
-    SkISize onISize() override {
-        return SkISize::Make(640, 480);
-    }
-
-    void onDraw(SkCanvas* canvas) override {
-        sk_test_c_api((sk_canvas_t*)canvas);
-    }
-
-private:
-    typedef GM INHERITED;
-};
-
-DEF_GM( return new C_GM; )
-
+DEF_SIMPLE_GM(c_gms, canvas, 640, 480) {
+    sk_test_c_api((sk_canvas_t*)canvas);
+}