community/fzf: rename -completion subpackages, switch to plugin convention & replace perl with awk in key-bindings.zsh

completion.{bash,zsh} are not completion functions for the fzf command command, but hooks into the shell completion system. Thus they shouldn't be installed in the locations for command completions, nor provided by *-{bash,zsh}-completion packages. It's not just semantically wrong, it even doesn't work for Zsh.

main/zsh now provides a simple plugin loader - when the plugin convention is followed, the user can easily load the fzf scripts just by creating a symlink ~/.local/share/zsh/plugins/fzf -> /usr/share/zsh/plugins/fzf or by adding ZSH_LOAD_SYSTEM_PLUGINS=yes into .zshenv or using a third-party plugin manager.

The same approach is now used in community/skim and most of the packages providing some Zsh plugin/extension (and a few for Bash plugins).