Use auto-alias for neutron-db-manage

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 alias
with 'snap alias'.

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

Change-Id: Iaac052b25bf2509bdb57161086a7be59d58de15f

README.md

@@ -69,14 +69,6 @@ well.
 The services for the neutron snap will log to its $SNAP_COMMON writable area:
 /var/snap/neutron/common/log.
 
-## Managing neutron
-
-The neutron snap has alias support that enables use of the well-known
-neutron-db-manage command. To enable the alias, run the following prior to
-using the command:
-
-    sudo snap alias neutron.manage neutron-db-manage
-
 ## Restarting neutron services
 
 To restart all neutron services:

snapcraft.yaml

@@ -13,8 +13,6 @@ apps:
       - network-bind
   manage:
     command: snap-openstack neutron-db-manage
-    aliases:
-      - neutron-db-manage
     plugs:
       - network