Fix UDP release note for CentOS

This patch removes the comment about the UDP patch not working on CentOS
because we fixed the issues that were impacting CentOS based amphora.

It also corrects a typo in the api-ref where the protocol field was listed
as an "integer" type, where it should be "string".

Change-Id: I0857015f25de607ab8364b9e1d59a65f8b072c3c

api-ref/source/parameters.yaml

@@ -842,7 +842,7 @@ protocol:
     ``TERMINATED_HTTPS``, or ``UDP``.
   in: body
   required: true
-  type: integer
+  type: string
 protocol-pools:
   description: |
     The protocol for the resource. One of ``HTTP``, ``HTTPS``, ``PROXY``,

releasenotes/notes/Add-UDP-protocol-support-9c011a23525092a1.yaml

@@ -7,7 +7,6 @@ issues:
   - You cannot mix IPv4 UDP listeners with IPv6 members at this time. This is
     being tracked with this story
     https://storyboard.openstack.org/#!/story/2003329
-  - CentOS based amphora images do not yet support UDP load balancing.
 upgrade:
   - |
     UDP protocol support requires an update to the amphora image to support