Remove senlin api doc metadata field
Remove senlin api doc metadata field

Senlin server code policy store data not exist metadata
field, The policy store data not need metadata field.

Change-Id: Ie351e7bb5eb32460852766ce47d598c299b0aaaa
Closes-Bug: 1760974

openstack/senlin,openstack/senlin,stackforge/senlin,openstack/senlin,stackforge/senlin