lavc/pthread: remove obsolete checks

Those were useful when avcodec_thread_init() was a public functions. It
was deprecated and removed some time ago, so those checks are not needed
anymore.

libavcodec/pthread.c

@@ -1042,23 +1042,16 @@ static void validate_thread_parameters(AVCodecContext *avctx)
 
 int ff_thread_init(AVCodecContext *avctx)
 {
-    if (avctx->thread_opaque) {
-        av_log(avctx, AV_LOG_ERROR, "avcodec_thread_init is ignored after avcodec_open\n");
-        return -1;
-    }
-
 #if HAVE_W32THREADS
     w32thread_init();
 #endif
 
-    if (avctx->codec) {
         validate_thread_parameters(avctx);
 
         if (avctx->active_thread_type&FF_THREAD_SLICE)
             return thread_init(avctx);
         else if (avctx->active_thread_type&FF_THREAD_FRAME)
             return frame_thread_init(avctx);
-    }
 
     return 0;
 }

libavcodec/utils.c

@@ -963,7 +963,7 @@ int attribute_align_arg avcodec_open2(AVCodecContext *avctx, const AVCodec *code
         avctx->time_base.den = avctx->sample_rate;
     }
 
-    if (HAVE_THREADS && !avctx->thread_opaque) {
+    if (HAVE_THREADS) {
         ret = ff_thread_init(avctx);
         if (ret < 0) {
             goto free_and_end;