Fix commitcheck on FreeBSD
Convert from bash to sh, avoid Perl regexes and \s, prune unused
functions.
Reviewed-by: Mateusz Piotrowski <0mp@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <freqlabs@FreeBSD.org>
Closes #11070