libass: remove enca as dependency
libass: remove enca as dependency

Enca support was dropped in 0.13.0: https://github.com/libass/libass/blob/6fc9855dac44699242ded580040838da032c3a9d/Changelog#L184

This also fixes cross-compilation, since enca didn't cross-compile.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs