avcodec/truehd_core_bsf: Remove unused AVClass pointer

The context structure of the truehd_core bsf had a pointer to a const
AVClass as its first member; yet this bsf does not have any AVClass
associated with it, so that this pointer is always NULL. So remove it.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/truehd_core_bsf.c

@@ -31,8 +31,6 @@ typedef struct AccessUnit {
 } AccessUnit;
 
 typedef struct TrueHDCoreContext {
-    const AVClass *class;
-
     MLPHeaderInfo hdr;
 } TrueHDCoreContext;