avcodec/cbs_h2645: use the fixed() macro for forbidden_zero_bit

This follows the spec definition, and removes a field from the relevant
structs.
Reviewed-by: Mark Thompson <sw@jkqxz.net>
Signed-off-by: James Almer <jamrial@gmail.com>

libavcodec/cbs_h264.h

@@ -38,7 +38,6 @@ enum {
 
 
 typedef struct H264RawNALUnitHeader {
-    uint8_t forbidden_zero_bit;
     uint8_t nal_ref_idc;
     uint8_t nal_unit_type;
 

libavcodec/cbs_h264_syntax_template.c

@@ -33,7 +33,7 @@ static int FUNC(nal_unit_header)(CodedBitstreamContext *ctx, RWContext *rw,
 {
     int err;
 
-    u(1, forbidden_zero_bit, 0, 0);
+    fixed(1, forbidden_zero_bit, 0);
     ub(2, nal_ref_idc);
     ub(5, nal_unit_type);
 

libavcodec/cbs_h265.h

@@ -35,7 +35,6 @@ enum {
 };
 
 typedef struct H265RawNALUnitHeader {
-    uint8_t forbidden_zero_bit;
     uint8_t nal_unit_type;
     uint8_t nuh_layer_id;
     uint8_t nuh_temporal_id_plus1;

libavcodec/cbs_h265_syntax_template.c

@@ -33,7 +33,7 @@ static int FUNC(nal_unit_header)(CodedBitstreamContext *ctx, RWContext *rw,
 {
     int err;
 
-    u(1, forbidden_zero_bit, 0, 0);
+    fixed(1, forbidden_zero_bit, 0);
 
     if (expected_nal_unit_type >= 0)
         u(6, nal_unit_type, expected_nal_unit_type,