* build: [gn] explicitly override rtc_use_h264
* build: [gn] don't override ffmpeg config from release config
* build: [gn] remove is_cfi override from release config
The original concern about node is fixed and we have been
building testing builds without the override for sometime now.
Devs can still locally override or add settings by adding lines after
the `import` statement in args.gn.
This will help make sure that everyone has a common set of build args,
and will allow us to update everyone's build args in git.