obs-filters: Remove unnecessary OBS_UNUSED attribute

The attribute OBS_UNUSED was added at 49e9d4994 but the parameter is
read in the function if LIBSPEEXDSP_ENABLED is defined

plugins/obs-filters/noise-suppress-filter.c

@@ -334,8 +334,8 @@ failure:
 }
 
 static inline void alloc_channel(struct noise_suppress_data *ng,
-				 uint32_t sample_rate OBS_UNUSED,
-				 size_t channel, size_t frames)
+				 uint32_t sample_rate, size_t channel,
+				 size_t frames)
 {
 #ifdef LIBSPEEXDSP_ENABLED
 	ng->spx_states[channel] =