ffmpeg: let ffmpeg choose necessary parsers for audio-dec and custom

This change allows ffmpeg's configure script to determine the necessary parsers based on
selected decoders & encoders. For libffmpeg-audio-dec, this changes from our selecting:

aac, ac3, flac, mpegaudio, opus and aac_latm

to ffmpeg's configure script selecting:

aac_latm, ac3, flac, mpegaudio

for minor space savings and a simpler Makefile to manage on our end.

In libffmpeg-custom, don't select any parsers when choosing decoders/encoders. I'm undecided
on removing the parser selection in its entirety here.

Signed-off-by: Ian Leonard <antonlacon@gmail.com>

multimedia/ffmpeg/Makefile

@@ -199,14 +199,6 @@ FFMPEG_AUDIO_DEMUXERS:= \
 	wav \
 	wv \
 
-FFMPEG_AUDIO_PARSERS:= \
-	aac \
-	aac_latm \
-	ac3 \
-	flac \
-	mpegaudio \
-	opus \
-
 FFMPEG_AUDIO_PROTOCOLS:= \
 	file http icecast rtp tcp udp
 
@@ -549,7 +541,6 @@ ifeq ($(BUILD_VARIANT),audio-dec)
 	--disable-everything \
 	$(call FFMPEG_ENABLE,decoder,$(FFMPEG_AUDIO_DECODERS)) \
 	$(call FFMPEG_ENABLE,demuxer,$(FFMPEG_AUDIO_DEMUXERS)) \
-	$(call FFMPEG_ENABLE,parser,$(FFMPEG_AUDIO_PARSERS)) \
 	$(call FFMPEG_ENABLE,protocol,$(FFMPEG_AUDIO_PROTOCOLS)) \
 	--disable-decoder=pcm_bluray,pcm_dvd \