lib/helpers: fix `all_groups()`

- Don't write to disk, just pipe.
- Don't loop, just do all functions.

Performance of old implementation on my system:
```
real    0m9.996s
user    0m5.318s
sys     0m9.126s
```

Performance of new implementation on my system:
```
real    0m0.052s
user    0m0.069s
sys     0m0.025s
```

lib/helpers.bash

@@ -1039,14 +1039,7 @@ all_groups ()
     about 'displays all unique metadata groups'
     group 'lib'
 
-    typeset func
+	declare -f | metafor group | sort -u
-    typeset file=$(mktemp -t composure.XXXX)
-    for func in $(_typeset_functions)
-    do
-        typeset -f $func | metafor group >> $file
-    done
-    cat $file | sort | uniq
-    rm $file
 }
 
 if ! type pathmunge > /dev/null 2>&1