Move `synapse_admin_hostname` to matrix_servers

Signed-off-by: Suguru Hirahara <did🔑z6MkvVZk1A3KBApWJXv2Ju4H14ErDfRGxh8zxdXSZ4vACDg5>

group_vars/matrix_servers

@@ -5175,6 +5175,8 @@ synapse_admin_config_asManagedUsers_auto: |
 
 synapse_admin_base_path: "{{ matrix_base_data_path }}/synapse-admin"
 
+synapse_admin_hostname: "{{ matrix_server_fqn_matrix }}"
+
 ######################################################################
 #
 # /synapse_admin

roles/custom/matrix-synapse-admin/defaults/main.yml

@@ -144,9 +144,6 @@ synapse_admin_floc_optout_enabled: true
 # See: `synapse_admin_http_header_strict_transport_security`
 synapse_admin_hsts_preload_enabled: false
 
-# The hostname at which Synapse Admin is served.
-synapse_admin_hostname: "{{ matrix_server_fqn_matrix }}"
-
 # The path at which Synapse Admin is exposed.
 # This value must either be `/` or not end with a slash (e.g. `/synapse-admin`).
 synapse_admin_path_prefix: /synapse-admin