Motown: Remove ffmpeg_branding arg to fix fnl build.

R=viettrungluu@chromium.org

Review URL: https://codereview.chromium.org/1924843002 .
diff --git a/mojo/tools/mopy/gn.py b/mojo/tools/mopy/gn.py
index b2e1fa8..deb29bc 100644
--- a/mojo/tools/mopy/gn.py
+++ b/mojo/tools/mopy/gn.py
@@ -54,9 +54,6 @@
   gn_args["is_official_build"] = bool(config.is_official_build)
   gn_args["is_asan"] = config.sanitizer == Config.SANITIZER_ASAN
 
-  if config.target_os != Config.OS_ANDROID:
-    gn_args["ffmpeg_branding"] = "ChromeOS"
-
   if config.is_clang is not None:
     gn_args["is_clang"] = bool(config.is_clang)
   else:
diff --git a/mojo/tools/mopy/gn_unittest.py b/mojo/tools/mopy/gn_unittest.py
index 7f07160..25bcaa4 100644
--- a/mojo/tools/mopy/gn_unittest.py
+++ b/mojo/tools/mopy/gn_unittest.py
@@ -54,12 +54,9 @@
       "mojo_use_nacl": [False, True],
       "mojo_use_go": [False],
       "dcheck_always_on": [False, True],
-      "ffmpeg_branding": ["ChromeOS"],
     }
 
     for args in _iterate_over_config(configs_to_test):
-      if args.get("target_os") == "android" and args["ffmpeg_branding"]:
-        continue
       config = gn.ConfigForGNArgs(args)
       new_args = gn.GNArgsForConfig(config)
       self.assertDictEqual(args, new_args)