Remove galera_client meta-dependency

Given that pymysql is pure python and has no C binding
dependencies, we no longer need the role to install the
MariaDB client libraries.

Change-Id: I309022aa53b8878a167d09d6288678eee5ca0159

meta/main.yml

@@ -42,6 +42,3 @@ dependencies:
   - role: apt_package_pinning
     when:
       - ansible_pkg_mgr == 'apt'
-  - role: galera_client
-    when:
-      - keystone_database_enabled | bool