build: fix ffmpeg gn gen (#19127)

* revert #18993

* build: fix ffmpeg GN gen

build/args/ffmpeg.gn

@@ -4,3 +4,4 @@ is_component_ffmpeg = true
 is_official_build = true
 proprietary_codecs = false
 ffmpeg_branding = "Chromium"
+enable_dsyms = false

script/run-gn-format.py

@@ -15,7 +15,6 @@ def main():
   for gn_file in sys.argv[1:]:
     subprocess.check_call(
       ['gn', 'format', gn_file],
-      shell=True,
       env=new_env
     )