systemd-tmpfiles: remove age-based cleanup of X11 socket directories (#42358)

Unexpected cleanup of live X11 socket files was reported in #35182,
suggesting an underlying issue with the `!` boot safety switch for
tmpfiles.

Regardless of that bug, time-based cleanup of X11 sockets is likely to
be unwanted behaviour as systems often stay up for extended periods of
time, and cleanup of these directories based on age alone is liable to
cause issues at runtime for user sessions.