Fix regular expression for exim logging to syslog.

[rjframe]

When exim writes to syslog the date and time are duplicated; e.g:

May 23 10:28:30 mx01 exim[27789]: 2019-05-23 10:28:30 1hTohn-0007EB-Nq Completed

I solved this by removing the match on newline; if that's desirable to keep, a regexp instead of the empty prefix would do it.