Removed 'api_paste_config' note from Nova controller section

Removed note about configuring 'api_paste_config' key in nova.conf
on controller node to agree with decision made during review of
patch for compute node.

https://review.openstack.org/#/c/78824/

Change-Id: I2249ff1115dc46a6d0d4ef47940d9e9cd68aa377
Closes-Bug: #1289493