shell-completion: zsh: fix incorrect unescaping

Previously the `_filter_units_by_property` completion function
outputs with a [zsh parameter expansion flag] `g⭕`. This means
that the returned result is unescaped as the zsh builtin `echo`,
except that octal escapes don’t take a leading zero. This seemed to
have worked back in the days when it was first introduced:

  6c9414a700

But it now leads to incorrect over-unescaping; for example,

  system-systemd\\x2djournald.slice (correct)

is incorrectly completed by zsh in commands such as
`systemctl kill`:

  system-systemd-journald.slice (incorrect)

This commit fixes such problems by removing the `g⭕` flag.

See:
[zsh parameter expansion flag]: https://zsh.sourceforge.io/Doc/Release/Expansion.html#Parameter-Expansion-Flags

shell-completion/zsh/_systemctl.in

@@ -190,7 +190,7 @@ __systemctl()
         local -a units; units=("${(q-)@}")
         local -A props
         props=(${(f)"$(_call_program units "$service $_sys_service_mgr show --no-pager --property=\"Id,$property\" -- ${units} 2>/dev/null")"})
-        echo -E - "${(@g:o:)${(k@)props[(Re)$property=$value]}#Id=}"
+        echo -E - "${(@)${(k@)props[(Re)$property=$value]}#Id=}"
     }
 
 (( $+functions[_systemctl_get_non_template_names] )) ||