Remove useless check

Since 025a5ab5e5f6bdb3, we do a similar check in matrix-base.

roles/matrix-dendrite/tasks/init.yml

@@ -5,8 +5,3 @@
 - set_fact:
     matrix_systemd_services_list: "{{ matrix_systemd_services_list + ['matrix-goofys.service'] }}"
   when: matrix_s3_media_store_enabled|bool
-
-- name: Fail when using also using Synapse
-  fail:
-    msg: "To use Dendrite as your matrix server, you should disable Synapse."
-  when: "matrix_dendrite_enabled and matrix_synapse_enabled"