[externals/ffmpeg] remove --disable-postproc causing issues in OpenOrbis toolchain (#3203)

why was disable-postproc added? either way this fixes build errors not only on PS4 but also on Haiku i think

Signed-off-by: lizzie lizzie@eden-emu.dev

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3203
Reviewed-by: Caio Oliveira <caiooliveirafarias0@gmail.com>
Co-authored-by: lizzie <lizzie@eden-emu.dev>
Co-committed-by: lizzie <lizzie@eden-emu.dev>

externals/ffmpeg/CMakeLists.txt

@@ -217,7 +217,6 @@ else()
                 --disable-ffmpeg
                 --disable-ffprobe
                 --disable-network
-                --disable-postproc
                 --disable-swresample
                 --enable-decoder=h264
                 --enable-decoder=vp8