audio: remove unused dcblocker

src/media/audio/CMakeLists.txt

src/media/audio/Makefile.am

src/media/audio/audiolayer.cpp

src/media/audio/audiolayer.h

src/media/audio/coreaudio/ios/corelayer.mm

src/media/audio/coreaudio/osx/corelayer.mm

src/media/audio/dcblocker.cpp

src/media/audio/dcblocker.h

src/media/audio/jack/jacklayer.cpp

src/media/audio/opensl/opensllayer.cpp

src/media/audio/portaudio/portaudiolayer.cpp

src/media/audio/pulseaudio/pulselayer.cpp

src/meson.build