Remove XML support from some server v3 API plugins

Remove XML support from the following v3 compute API plugins:

 - security_groups
 - server_diagnostics
 - server_metadata
 - server_password
 - server_usage

Part of blueprint remove-v3-xml-api

DocImpact

Change-Id: If3e8d82d6db2a2ff328ba477bffd5081f098be9a
Merge "Remove XML support from some server v3 API plugins"