doc: remove module index
doc: remove module index

Remove the broken link to non existing module documentation.

Change-Id: Ife63d07f6e1c41ae6d6e602aceb7d830effbe3e0
Closes-Bug: 1656400

stackforge/networking-bagpipe-l2,openstack/networking-bagpipe,openstack/networking-bagpipe,openstack/networking-bagpipe-l2,stackforge/networking-bagpipe-l2,openstack/networking-bagpipe-l2