zsh: use sys_really_all_units for non-template names

The systemctl invocations used for these completions match the ones used
for the _sys_really_all_units parameter, so we should really just use
the cached parameter rather than recomputing the result.

(cherry picked from commit c8e2cd7)
(cherry picked from commit 9814972)

Author: rpigott

shell-completion/zsh/_systemctl.in

@@ -193,10 +193,10 @@ __systemctl()
     }
 
 (( $+functions[_systemctl_get_non_template_names] )) ||
-    _systemctl_get_non_template_names() { echo -E - ${^${(R)${(f)"$(
-    __systemctl list-unit-files
-    __systemctl list-units --all
-  )"}:#*@.*}%%[[:space:]]*} }
+    _systemctl_get_non_template_names() {
+        _systemctl_really_all_units
+        print -r - ${_sys_really_all_units:#*@.*}
+    }
 
 (( $+functions[_systemctl_get_template_names] )) ||
     _systemctl_get_template_names() { echo -E - ${^${(M)${(f)"$(__systemctl list-unit-files)"}##*@.[^[:space:]]##}%%@.*}\@ }