Remove libavdevice on Windows, too. Other platforms: Remove libavdevice headers.

It's not actually needed for compilation/functionality of PPSSPP on Windows, like other platforms.

https://github.com/hrydgard/ppsspp-ffmpeg/commit/8c7314c37d594b299a32fc4d2865e82d84b5e23c#commitcomment-4435148

Removed OSX and iOS libavdevice libs and all other platforms' headers at @xsacha's request.