Remove 'nova-xvpvncproxy'

This legacy service is no longer used and was deprecated during the
Stein cycle [1]. It's time to say adios and remove them in their
entirety. This is pretty straightforward, with the sole exception of
schema for the 'remote-consoles' API, which has to continue supporting
requests for type 'xvpvnc' even if we can't fulfil those requests now.

[1] https://review.opendev.org/#/c/610076/

Part of blueprint remove-xvpvncproxy

Depends-On: https://review.opendev.org/695853
Change-Id: I2f7f2379d0cd54e4d0a91008ddb44858cfc5a4cf
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>

api-guide/source/server_concepts.rst

@@ -783,12 +783,11 @@ Server Consoles
 Server Consoles can also be supplied after server launched. There are several
 server console services available. First, users can get the console output
 from the specified server and can limit the lines of console text by setting
-the length. Second, users can access multiple types of remote consoles. The
-user can use novnc, xvpvnc, rdp-html5, spice-html5, serial, and webmks(start
-from microversion 2.8) through either the OpenStack dashboard or the command
-line. Refer to :nova-doc:`Configure remote console access
-<admin/remote-console-access.html>`.  Specifically for Xenserver, it provides
-the ability to create, delete, detail, list specified server vnc consoles.
+the length. Secondly, users can access multiple types of remote consoles. The
+user can use ``novnc``, ``rdp-html5``, ``spice-html5``, ``serial``, and
+``webmks`` (starting from microversion 2.8) through either the OpenStack
+dashboard or the command line. Refer to :nova-doc:`Configure remote console
+access <admin/remote-console-access.html>`.
 
 Server networks
 ~~~~~~~~~~~~~~~