completions: use standard fish functions for subcommands

pkg/omf/completions/omf.fish

 # SYNOPSIS
 #   Completions for Oh My Fish CLI
 
-function __omf.is_single_opt
-  test (count (commandline -opc)) -le 1
-end
+complete -c omf -f -d "Oh My Fish"
 
-function __omf.opt_is
-  set -l cmd (commandline -opc)
-  test (count $cmd) -gt 1; and contains -- $cmd[2] $argv
-end
+complete -c omf -f -n "__fish_seen_subcommand_from q query"         -a (printf "%s " (set | awk '{ printf $1"\n"; }'))
+complete -c omf -f -n "__fish_seen_subcommand_from r rm remove"     -a (printf "%s " (omf.list_local_packages) (omf.list_installed_themes))
+complete -c omf -f -n "__fish_seen_subcommand_from d desc describe" -a (printf "%s " (omf.list_db_packages))
+complete -c omf -f -n "__fish_seen_subcommand_from c cd"            -a (printf "%s " (omf.list_db_packages))
+complete -c omf -f -n "__fish_seen_subcommand_from i install"       -a (printf "%s " (omf.list_db_packages "skip installed packages"))
+complete -c omf -f -n "__fish_seen_subcommand_from t theme"         -a (printf "%s " (omf.list_themes))
+complete -c omf -f -n "__fish_seen_subcommand_from help"            -a "install theme remove update list describe cd new submit query destroy"
 
-complete --no-files -c omf -d "Oh My Fish"
-
-complete -c omf -n "__omf.opt_is q query"         -a (printf "%s " (set | awk '{ printf $1"\n"; }'))
-complete -c omf -n "__omf.opt_is r rm remove"     -a (printf "%s " (omf.list_local_packages) (omf.list_installed_themes))
-complete -c omf -n "__omf.opt_is d desc describe" -a (printf "%s " (omf.list_db_packages))
-complete -c omf -n "__omf.opt_is c cd"            -a (printf "%s " (omf.list_db_packages))
-complete -c omf -n "__omf.opt_is i install"       -a (printf "%s " (omf.list_db_packages "skip installed packages"))
-complete -c omf -n "__omf.opt_is t theme"         -a (printf "%s " (omf.list_themes))
-complete -c omf -n "__omf.opt_is help"            -a "install theme remove update list describe cd new submit query destroy"
-
-complete -c omf -a list     -n "__omf.is_single_opt" -d "List local packages"
-complete -c omf -a describe -n "__omf.is_single_opt" -d "Get information about what packages do"
-complete -c omf -a install  -n "__omf.is_single_opt" -d "Install one or more packages"
-complete -c omf -a theme    -n "__omf.is_single_opt" -d "List / Use themes"
-complete -c omf -a remove   -n "__omf.is_single_opt" -d "Remove a theme or package"
-complete -c omf -a update   -n "__omf.is_single_opt" -d "Update Oh My Fish"
-complete -c omf -a cd       -n "__omf.is_single_opt" -d "Change directory to plugin/theme directory"
-complete -c omf -a new      -n "__omf.is_single_opt" -d "Create a new package from a template"
-complete -c omf -a submit   -n "__omf.is_single_opt" -d "Submit a package to the registry"
-complete -c omf -a query    -n "__omf.is_single_opt" -d "Query environment variables"
-complete -c omf -a help     -n "__omf.is_single_opt" -d "Display this help"
-complete -c omf -a version  -n "__omf.is_single_opt" -d "Display version"
-complete -c omf -a destroy  -n "__omf.is_single_opt" -d "Remove Oh My Fish"
+complete -c omf -f -a list     -n "__fish_use_subcommand" -d "List local packages"
+complete -c omf -f -a describe -n "__fish_use_subcommand" -d "Get information about what packages do"
+complete -c omf -f -a install  -n "__fish_use_subcommand" -d "Install one or more packages"
+complete -c omf -f -a theme    -n "__fish_use_subcommand" -d "List / Use themes"
+complete -c omf -f -a remove   -n "__fish_use_subcommand" -d "Remove a theme or package"
+complete -c omf -f -a update   -n "__fish_use_subcommand" -d "Update Oh My Fish"
+complete -c omf -f -a cd       -n "__fish_use_subcommand" -d "Change directory to plugin/theme directory"
+complete -c omf -f -a new      -n "__fish_use_subcommand" -d "Create a new package from a template"
+complete -c omf -f -a submit   -n "__fish_use_subcommand" -d "Submit a package to the registry"
+complete -c omf -f -a query    -n "__fish_use_subcommand" -d "Query environment variables"
+complete -c omf -f -a help     -n "__fish_use_subcommand" -d "Display this help"
+complete -c omf -f -a version  -n "__fish_use_subcommand" -d "Display version"
+complete -c omf -f -a destroy  -n "__fish_use_subcommand" -d "Remove Oh My Fish"