avresample: remove deprecated attribute from the AVAudioResampleContext struct

Having all the public functions marked as deprecated is enough.

This gets rid of a warning spam when compiling any file including
libavresample/avresample.h even when avresample is not enabled, like
it's the case with fftools/cmdutils.c

Signed-off-by: James Almer <jamrial@gmail.com>

libavresample/avresample.h

@@ -103,7 +103,7 @@
 
 #define AVRESAMPLE_MAX_CHANNELS 32
 
-typedef attribute_deprecated struct AVAudioResampleContext AVAudioResampleContext;
+typedef struct AVAudioResampleContext AVAudioResampleContext;
 
 /**
  * @deprecated use libswresample