refactor: improve `fisher rm` completions

For tab completions we want to list only the packages that you
added yourself (via the CLI or fishfile) and ignore those that
are installed but are dependencies of another package/s.

fisher.fish

@@ -79,12 +79,15 @@ function _fisher_self_complete
     complete -ec fisher
     complete -xc fisher -n __fish_use_subcommand -a add -d "Add packages"
     complete -xc fisher -n __fish_use_subcommand -a rm -d "Remove packages"
-    complete -xc fisher -n __fish_use_subcommand -a ls -d "List added packages"
+    complete -xc fisher -n __fish_use_subcommand -a ls -d "List installed packages"
     complete -xc fisher -n __fish_use_subcommand -a help -d "Show usage help"
     complete -xc fisher -n __fish_use_subcommand -a version -d "$fisher_version"
     complete -xc fisher -n __fish_use_subcommand -a self-update -d "Update to the latest version"
+    set -l file (_fisher_fmt < $fisher_path/fishfile | _fisher_read)
     for pkg in (_fisher_ls | _fisher_fmt)
-        complete -xc fisher -n "__fish_seen_subcommand_from rm" -a $pkg
+        if contains -- $pkg $file
+            complete -xc fisher -n "__fish_seen_subcommand_from rm" -a $pkg
+        end
     end
 end
 
@@ -260,7 +263,7 @@ function _fisher_read -a cmd
             if (CMD == "rm") {
                 for (pkg in pkgs) {
                     if (!(pkg in file)) {
-                        print "cannot remove \"" pkg "\" -- package not found" > "/dev/stderr"
+                        print "cannot remove \""pkg"\" -- package not listed in fishfile" > "/dev/stderr"
                     }
                 }
             }