MDEV-34430: remove Debian character-set-collations

Since MDEV-25829 Change default Unicode collation to uca1400_ai_ci
there is no need to set character-set-collations explicitly as its
the default.

Further mode the change in defaults affects all character sets that
support the uca1400_ai_ci collation.

debian/additions/mariadb.conf.d/50-server.cnf

@@ -87,7 +87,6 @@ expire_logs_days        = 10
 # MariaDB default is Latin1, but in Debian we rather default to the full
 # utf8 4-byte character set. See also client.cnf
 character-set-server     = utf8mb4
-character-set-collations = utf8mb4=uca1400_ai_ci
 
 #
 # * InnoDB