buildscripts/README: remove no longer relevant sentence
buildscripts/README: remove no longer relevant sentence

Clang is now the default, and the override we have for GCC is only
for testing, and not generally recommended.

mpv-android/mpv-android,mpv-android/mpv-android,mpv-android/mpv-android,mpv-android/mpv-android,mpv-android/mpv-android,jeeb/mpv-android,jeeb/mpv-android,jeeb/mpv-android,jeeb/mpv-android,jeeb/mpv-android