all: remove unused functions from includes

Signed-off-by: Mahyar Koshkouei <mk@deltabeard.com>

include/opus.h

@@ -2,19 +2,4 @@
 #include "playback.h"
 
 void setOpus(struct decoder_fn* decoder);
-
-int initOpus(const char* file);
-
-uint32_t rateOpus(void);
-
-uint8_t channelOpus(void);
-
-uint64_t decodeOpus(void* buffer);
-
-void exitOpus(void);
-
-int playOpus(const char* in);
-
-uint64_t fillOpusBuffer(int16_t* bufferOut);
-
 int isOpus(const char* in);