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: I3d752bdde0dc38fd0cf4a5941b9d4496189dddb7

meta/main.yml

@@ -40,6 +40,3 @@ dependencies:
   - role: apt_package_pinning
     when:
       - ansible_pkg_mgr == 'apt'
-  - role: galera_client
-    vars:
-      galera_client_drop_config_file: false