Migrate to new --completion command

[pd93]

Description

In #1157, a new --completion flag was added to Task and we deprecated the direct use of the files in the /completions directory.

The next step for completions is to delete the existing files from the project and migrate them to templates. This will give us more flexibility to dynamically add commands/flags to the scripts. However, this cannot be done until users have moved away from the existing completion scripts (unless we duplicate them I guess).

This issue is a rollup to track which installation methods are still using the deprecated completions method and which have migrated to the new flag.

• Homebrew (Tap) [source] - feat: update homebrew to use generate_completions_from_executable #1990
• Homebrew (Official) [source] - Migration needed
• Snap [source] - No completions
• npm [source] - No completions
• Winget [source] - No completions
• Chocolatey [source] - No completions
• Scoop [source] - No completions
• Arch (pacman) [source] - Migration needed
• Fedora (dnf) [source] - No completions
• Nix [source] - go-task: update shell completions NixOS/nixpkgs#370166
• Pacstall [source] - No completions
• pkgx [source] - No completions