mpvScripts: update convert script patch to work with current mpv

[Profpatsch]

mpv has finally made some options an error that they removed in 0.30,
a few versions ago.

Plus, refactors the tool overrides a bit.

Fixes #113202

Motivation for this change

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[r-rmcgibbo]

Result of nixpkgs-review pr 120246 at 72cc405 run on x86_64-linux 1

1 package built successfully:

• mpvScripts.convert

1 suggestion:

• warning: missing-patch-comment

  Please add a comment on the line above, explaining the purpose of this patch.
  Near pkgs/applications/video/mpv/scripts/convert.nix:13:15:

     |
  13 |   patches = [ ./convert.patch ];
     |               ^