Remove MariaDB support (#3381)

doc/admin/config.rst

@@ -154,23 +154,15 @@ Example::
     port=3306
 
 ``backend``
-    One of ``mysql`` (deprecated), ``sqlite3`` and ``postgresql``.
+    One of ``sqlite3`` and ``postgresql``.
     Default: ``sqlite3``.
 
-    If you use MySQL, be sure to create your database using
-    ``CREATE DATABASE <dbname> CHARACTER SET utf8;``. Otherwise, Unicode
-    support will not properly work.
-
 ``name``
     The database's name. Default: ``db.sqlite3``.
 
 ``user``, ``password``, ``host``, ``port``
     Connection details for the database connection. Empty by default.
 
-``galera``
-    (Deprecated) Indicates if the database backend is a MySQL/MariaDB Galera cluster and
-    turns on some optimizations/special case handlers. Default: ``False``
-
 .. _`config-replica`:
 
 Database replica settings

doc/admin/installation/general.rst

@@ -16,14 +16,11 @@ To use pretix, you will need the following things:
 * A periodic task runner, e.g. ``cron``
 
 * **A database**. This needs to be a SQL-based that is supported by Django. We highly recommend to either
-  go for **PostgreSQL** or **MySQL/MariaDB**. If you do not provide one, pretix will run on SQLite, which is useful
+  go for **PostgreSQL**. If you do not provide one, pretix will run on SQLite, which is useful
   for evaluation and development purposes.
 
   .. warning:: Do not ever use SQLite in production. It will break.
 
-  .. warning:: We recommend **PostgreSQL**. If you go for MySQL, make sure you run **MySQL 5.7 or newer** or
-               **MariaDB 10.2.7 or newer**.
-
 * A **reverse proxy**. pretix needs to deliver some static content to your users (e.g. CSS, images, ...). While pretix
   is capable of doing this, having this handled by a proper web server like **nginx** or **Apache** will be much
   faster. Also, you need a proxying web server in front to provide SSL encryption.

doc/admin/mysql2postgres.rst

@@ -3,11 +3,11 @@
 Migrating from MySQL/MariaDB to PostgreSQL
 ==========================================
 
-Our recommended database for all production installations is PostgreSQL. Support for MySQL/MariaDB will be removed in
-pretix 5.0.
+Our recommended database for all production installations is PostgreSQL. Support for MySQL/MariaDB has been removed
+in newer pretix releases.
 
 In order to follow this guide, your pretix installation needs to be a version that fully supports MySQL/MariaDB. If you
-already upgraded to pretix 5.0, downgrade back to the last 4.x release using ``pip``.
+already upgraded to pretix 5.0 or later, downgrade back to the last 4.x release using ``pip``.
 
 .. note:: We have tested this guide carefully, but we can't assume any liability for its correctness. The data loss
           risk should be low as long as pretix is not running while you do the migration. If you are a pretix Enterprise