contrib: ffmpeg: remove no-op --enable-neon

This is the default, and has no actual effects. The FFmpeg configure
script will check if NEON is supported *unless* given --disable-neon is
passed.

By comparison, the ARMv6 condition below is correct (at least in this
respect) in forcefully disabling NEON.

contrib/src/ffmpeg/rules.mak

@@ -81,9 +81,6 @@ endif
 # ARM stuff
 ifeq ($(ARCH),arm)
 FFMPEGCONF += --arch=arm
-ifdef HAVE_NEON
-FFMPEGCONF += --enable-neon
-endif
 ifdef HAVE_ARMV7A
 FFMPEGCONF += --cpu=cortex-a8
 endif