contrib: ffmpeg: remove gas-preprocessor on Android

Build vlc-android on macOS was broken since gas-preprocessor fix_unreq
is enabled by default on macOS.
13 jobs for !5 with patch-no-gaspp-ffmpeg in 55 minutes and 46 seconds (queued for 5 seconds)
detached
Status Job ID Name Coverage
  Build
passed #321402
amd64 docker
android-arm

00:13:44

passed #321403
amd64 docker
android-arm64

00:14:01

passed #322119
docker amd64
android-x86

00:14:34

passed #321405
amd64 docker
android-x86_64

00:12:20

passed #322121
docker amd64
debian

00:10:29

passed #321401
macos
ios-arm64

00:17:24

passed #321400
macos
macos

00:37:40

passed #321396
amd64 docker
win32

00:24:19

passed #321397
amd64 docker
win64

00:25:45

passed #322120
docker amd64
win64-llvm

00:18:04

failed #321404
amd64 docker
android-x86

00:09:46

failed #321399
amd64 docker
debian

00:10:58

failed #321398
amd64 docker
win64-llvm

00:26:18