MDEV-9227 : Both CentOS service names mysql and mariadb exist?

As 10.1 has systemd support, there is no longer need to set
_SYSTEMCTL_SKIP_REDIRECT/SYSTEMD_NO_WRAP.

debian/mariadb-server-10.1.mysql.init

@@ -17,9 +17,6 @@ set -e
 set -u
 ${DEBIAN_SCRIPT_DEBUG:+ set -v -x}
 
-# Prevent Debian's init scripts from calling systemctl
-_SYSTEMCTL_SKIP_REDIRECT=true
-
 test -x /usr/sbin/mysqld || exit 0
 
 . /lib/lsb/init-functions

support-files/mysql.server.sh

@@ -25,14 +25,6 @@
 # Description: MySQL is a very fast and reliable SQL database engine.
 ### END INIT INFO
 
-# Prevent OpenSUSE's init scripts from calling systemd, so that
-# both 'bootstrap' and 'start' are handled entirely within this
-# script
-SYSTEMD_NO_WRAP=1
-
-# Prevent Debian's init scripts from calling systemctl
-_SYSTEMCTL_SKIP_REDIRECT=true
- 
 # If you install MySQL on some other places than @prefix@, then you
 # have to do one of the following things for this script to work:
 #