mpeg4audio: rename AOT_USAC_NOSBR to AOT_USAC

The issue is that AOT 45 isn't defined anywhere, and looking at the git
blame, it seems to have sprung up through a reordering of the enum,
and adding a hole.

The spec does not define an explicit AOT for SBR and no SBR, and only
uses AOT 42 (previously AOT_USAC_NOSBR), so just rename AOT_USAC to
it and replace its use everywhere.

libavcodec/aac/aacdec.c

@@ -1046,7 +1046,6 @@ static int decode_audio_specific_config_gb(AACDecContext *ac,
             return ret;
         break;
 #if CONFIG_AAC_DECODER
-    case AOT_USAC_NOSBR: /* fallthrough */
     case AOT_USAC:
         if ((ret = ff_aac_usac_config_decode(ac, avctx, gb,
                                              oc, m4ac->chan_config)) < 0)
@@ -1571,8 +1570,7 @@ int ff_aac_decode_tns(AACDecContext *ac, TemporalNoiseShaping *tns,
                       GetBitContext *gb, const IndividualChannelStream *ics)
 {
     int tns_max_order = INT32_MAX;
-    const int is_usac = ac->oc[1].m4ac.object_type == AOT_USAC ||
-                        ac->oc[1].m4ac.object_type == AOT_USAC_NOSBR;
+    const int is_usac = ac->oc[1].m4ac.object_type == AOT_USAC;
     int w, filt, i, coef_len, coef_res, coef_compress;
     const int is8 = ics->window_sequence[0] == EIGHT_SHORT_SEQUENCE;
 
@@ -2421,8 +2419,7 @@ static int aac_decode_frame_int(AVCodecContext *avctx, AVFrame *frame,
 
     ac->tags_mapped = 0;
 
-    if ((ac->oc[1].m4ac.object_type == AOT_USAC) ||
-        (ac->oc[1].m4ac.object_type == AOT_USAC_NOSBR)) {
+    if (ac->oc[1].m4ac.object_type == AOT_USAC) {
         if (ac->is_fixed) {
             avpriv_report_missing_feature(ac->avctx,
                                           "AAC USAC fixed-point decoding");

libavcodec/mpeg4audio.h

@@ -108,10 +108,9 @@ enum AudioObjectType {
     AOT_ER_AAC_ELD,            ///< N                       Error Resilient Enhanced Low Delay
     AOT_SMR_SIMPLE,            ///< N                       Symbolic Music Representation Simple
     AOT_SMR_MAIN,              ///< N                       Symbolic Music Representation Main
-    AOT_USAC_NOSBR,            ///< N                       Unified Speech and Audio Coding (no SBR)
+    AOT_USAC,                  ///< Y                       Unified Speech and Audio Coding
     AOT_SAOC,                  ///< N                       Spatial Audio Object Coding
     AOT_LD_SURROUND,           ///< N                       Low Delay MPEG Surround
-    AOT_USAC,                  ///< N                       Unified Speech and Audio Coding
 };
 
 #define MAX_PCE_SIZE 320 ///<Maximum size of a PCE including the 3-bit ID_PCE