MDEV-15526 systemd unit files naming and installation

Drop Aliases from the service file directive. Aliases in the service
file only take effect when the service is enabled. This is the case
because Aliases in service files do not have to be unique across various
services.

Shipping symlinks guarantees that one can always enable mariadb service
using `systemctl enable mysql` or `systemctl enable mysqld` and makes
the commands indempotent.

debian/mariadb-server-10.5.links

+lib/systemd/system/mariadb.service lib/systemd/system/mysql.service                                                                                                                                                 
+lib/systemd/system/mariadb.service lib/systemd/system/mysqld.service
 usr/bin/mariadb-binlog usr/bin/mysqlbinlog
 usr/bin/mariadb-convert-table-format usr/bin/mysql_convert_table_format
 usr/bin/mariadb-hotcopy usr/bin/mysqlhotcopy

support-files/mariadb.service.in

@@ -26,8 +26,6 @@ After=network.target
 
 [Install]
 WantedBy=multi-user.target
-Alias=mysql.service
-Alias=mysqld.service
 
 
 [Service]