Use auto-alias for neutron-*-cleanup

The current snaps now have well-known aliases defined at install time
for commands [1]. This means we can drop the manual alias definition
from snapcraft.yaml and the instructions for setting it up.

When building/installing locally users can still create the aliases
with 'snap alias'.

[1] https://forum.snapcraft.io/t/auto-aliases-for-openstack-base-snaps/1146/6

Change-Id: I2eef1705d5e1c01e4f8b76ebdbbaf64374df7272

README.md

@@ -122,13 +122,6 @@ following plugs and slots must be connected:
     sudo snap connect nova-hypervisor:network-control core:network-control
     sudo snap connect nova-hypervisor:firewall-control core:firewall-control
 
-The nova-hypervisor snap has alias support that enables use of the well-known
-neutron-netns-cleanup and neutron-ovs-cleanup commands. To enable the aliases,
-run the following prior to using the commands:
-
-    sudo snap alias nova-hypervisor.neutron-netns-cleanup neutron-netns-cleanup
-    sudo snap alias nova-hypervisor.neutron-ovs-cleanup neutron-ovs-cleanup
-
 ## Restarting services
 
 To restart all nova-hypervisor services:

snapcraft.yaml

@@ -81,16 +81,12 @@ apps:
       - network-control
   neutron-ovs-cleanup:
     command: snap-openstack neutron-ovs-cleanup
-    aliases:
-      - neutron-ovs-cleanup
     plugs:
       - network
       - network-control
       - openvswitch
   neutron-netns-cleanup:
     command: snap-openstack neutron-netns-cleanup
-    aliases:
-      - neutron-netns-cleanup
     plugs:
       - network
       - network-control