audio/filter: remove some useless filters

All of these filters are considered not useful anymore by us. Some have
replacements in libavfilter (useable through af_lavfi).

af_center, af_extrastereo, af_karaoke, af_sinesuppress, af_sub,
af_surround, af_sweep: pretty simple and useless filters which probably
nobody ever wants.

af_ladspa: has a replacement in libavfilter.

af_hrtf: the algorithm doesn't work properly on most sources, and the
implementation was buggy and complicated. (The filter was inherited from
MPlayer; but even in mpv times we had to apply fixes that fixed major
issues with added noise.) There is a ladspa filter if you still want to
use it.

af_export: I'm not even sure what this is supposed to do. Possibly it
was meant for GUIs rendering audio visualizations, but it couldn't
really work well. For example, the size of the audio depended on the
samplerate (fixed number of samples only), and it couldn't retrieve the
complete audio, only fragments. If this is really needed for GUIs, mpv
should add native visualization, or a proper API for it.

TOOLS/old-configure

@@ -191,7 +191,6 @@ options_state_machine() {
     opt_yes_no _libcdio     "libcdio support"
     opt_yes_no _librubberband "librubberband support"
     opt_yes_no _ffmpeg      "skip FFmpeg/Libav autodetection"
-    opt_yes_no _ladspa      "LADSPA plugin support"
     opt_yes_no _libbs2b     "libbs2b audio filter support"
     opt_yes_no _libavresample "libavresample (preferred over libswresample)"
     opt_yes_no _libswresample "libswresample"
@@ -749,9 +748,6 @@ check_pkg_config "uchardet" $_uchardet UCHARDET 'uchardet'
 check_pkg_config "zlib" auto ZLIB 'zlib'
 test $(defretval) = no && die "Unable to find development files for zlib."
 
-test "$_dl" = no && _ladspa=no
-check_statement_libs "LADSPA plugin support" $_ladspa LADSPA ladspa.h 'LADSPA_Descriptor ld = {0}'
-
 check_pkg_config "libbs2b audio filter support" $_libbs2b LIBBS2B 'libbs2b'
 
 check_pkg_config "LCMS2 support" $_lcms2 LCMS2 'lcms2 >= 2.6'

TOOLS/old-makefile

@@ -35,7 +35,6 @@ SOURCES-$(DVDREAD)              += stream/stream_dvd.c \
 SOURCES-$(DVDNAV)               += stream/stream_dvdnav.c \
                                    stream/stream_dvd_common.c
 
-SOURCES-$(LADSPA)               += audio/filter/af_ladspa.c
 SOURCES-$(RUBBERBAND)           += audio/filter/af_rubberband.c
 SOURCES-$(LIBASS)               += sub/ass_mp.c sub/sd_ass.c \
                                    demux/demux_libass.c
@@ -123,28 +122,17 @@ SOURCES = audio/audio.c \
           audio/decode/ad_spdif.c      \
           audio/decode/dec_audio.c \
           audio/filter/af.c \
-          audio/filter/af_center.c \
           audio/filter/af_channels.c \
           audio/filter/af_delay.c \
           audio/filter/af_equalizer.c \
-          audio/filter/af_export.c \
-          audio/filter/af_extrastereo.c \
           audio/filter/af_format.c \
-          audio/filter/af_hrtf.c \
-          audio/filter/af_karaoke.c \
           audio/filter/af_lavcac3enc.c \
           audio/filter/af_lavrresample.c \
           audio/filter/af_pan.c \
           audio/filter/af_scaletempo.c \
-          audio/filter/af_sinesuppress.c \
-          audio/filter/af_sub.c \
-          audio/filter/af_surround.c \
-          audio/filter/af_sweep.c \
           audio/filter/af_drc.c \
           audio/filter/af_volume.c \
-          audio/filter/filter.c \
           audio/filter/tools.c \
-          audio/filter/window.c \
           audio/out/ao.c \
           audio/out/ao_null.c \
           audio/out/ao_pcm.c \