Drop enable-host-header config option

Enable this option as an opinionated default that works well
with a charm based deployment.

This ensures that the href to the designate API reflects the
endpoint binding that the service was access over.

Drop exposure as a configuration option.

Change-Id: Ic4c29404335aff9a0f66f45ef41c3862035b4a4d
Closes-Bug: 1805707

src/config.yaml

@@ -63,10 +63,6 @@ options:
     description: |
       Format of floating IPv6 global records.
       (NOTE: This option is obsolete starting from OpenStack Mitaka release)
-  enable-host-header:
-    type: boolean
-    default: false
-    description: Enables host request headers.
   also-notifies:
     type: string
     default:

src/templates/mitaka/designate.conf

@@ -80,7 +80,7 @@ workers = {{ options.workers }}
 #threads = 1000
 
 # Enable host request headers
-enable_host_header = {{ options.enable_host_header }}
+enable_host_header = true
 
 # The base uri used in responses
 api_base_uri = '{{ options.external_endpoints.designate_api.url }}'

src/templates/rocky/designate.conf

@@ -78,7 +78,7 @@ workers = {{ options.workers }}
 #threads = 1000
 
 # Enable host request headers
-enable_host_header = {{ options.enable_host_header }}
+enable_host_header = true
 
 # The base uri used in responses
 api_base_uri = '{{ options.external_endpoints.designate_api.url }}'