Deprecate ineffective [service:api] max_header_line

This parmaeter has had no effect since [1] was merged. Because
the parmaeter has been broken for several cycles and there has been
the alternative parameter ([DEFAULT] max_header_line) to configure
the same, this change makes the parameter for removal instead of fixing
it.

[1] a09064a5d1

Closes-Bug: #1967825
Change-Id: I04ea6b8132e6aee35eb72992273f63f3512d4aeb

designate/conf/api.py

@@ -46,6 +46,10 @@ API_OPTS = [
     cfg.BoolOpt('enable_api_admin', default=False,
                 help='enable-api-admin'),
     cfg.IntOpt('max_header_line', default=16384,
+               deprecated_for_removal=True,
+               deprecated_reason='This parameter has had no effect since '
+                                 'Train. Use [DEFAULT] max_header_line '
+                                 'instead.',
                help="Maximum line size of message headers to be accepted. "
                     "max_header_line may need to be increased when using "
                     "large tokens (typically those generated by the "

releasenotes/notes/bug-1967825-c3463edde9a9dd7a.yaml

@@ -0,0 +1,7 @@
+---
+deprecations:
+  - |
+    The ``[service:api] max_header_line`` parameter has been deprecated. This
+    parameter has hd no effect since the Train release. Use
+    the ``[DEFAULT] max_header_line`` parameter of the ``oslo.service`` library
+    instead.