vf_sub: undeprecate

3a9e661e92 officially made this video
filter deprecated roughly 6 years ago. Every other video filter in that
commit has actually been removed since then except for vf_sub. ffmpeg
does have its own subtitles filter, but it doesn't have the same control
over scale like vf_sub does. That's probably why wm4 never actually
removed it. Let's stop scaring users with a warning since this filter
probably won't ever get removed. Closes #9254.

DOCS/interface-changes.rst

@@ -51,6 +51,7 @@ Interface changes
       dpi scale factor by default (can be disabled with --no-hidpi-window-scale
       if fractional scaling support exists).
     - change --screenshot-tag-colorspace default value from `no` to `yes`
+    - undeprecate vf_sub
  --- mpv 0.35.0 ---
     - add the `--vo=gpu-next` video output driver, as well as the options
       `--allow-delayed-peak-detect`, `--builtin-scalers`,

video/filter/vf_sub.c

@@ -139,8 +139,6 @@ static struct mp_filter *vf_sub_create(struct mp_filter *parent, void *options)
         return NULL;
     }
 
-    MP_WARN(f, "This filter is deprecated and will be removed (no replacement)\n");
-
     mp_filter_add_pin(f, MP_PIN_IN, "in");
     mp_filter_add_pin(f, MP_PIN_OUT, "out");