avfilter: Remove init_opaque callback

The last init_opaque callback has been removed in commit
07ffdedf784e86b88074d8d3e08e55752869562a; the opaque argument has been
always NULL since 0acf7e268b.

Reviewed-by: Nicolas George <george@nsup.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavfilter/avfilter.c

@@ -877,9 +877,7 @@ int avfilter_init_dict(AVFilterContext *ctx, AVDictionary **options)
         }
     }
 
-    if (ctx->filter->init_opaque)
-        ret = ctx->filter->init_opaque(ctx, NULL);
-    else if (ctx->filter->init)
+    if (ctx->filter->init)
         ret = ctx->filter->init(ctx);
     else if (ctx->filter->init_dict)
         ret = ctx->filter->init_dict(ctx, options);

libavfilter/avfilter.h

@@ -300,13 +300,6 @@ typedef struct AVFilter {
      */
     int (*process_command)(AVFilterContext *, const char *cmd, const char *arg, char *res, int res_len, int flags);
 
-    /**
-     * Filter initialization function, alternative to the init()
-     * callback. Args contains the user-supplied parameters, opaque is
-     * used for providing binary data.
-     */
-    int (*init_opaque)(AVFilterContext *ctx, void *opaque);
-
     /**
      * Filter activation function.
      *