Use auto-alias for nova-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: Iab9fce6b31aaf4d135317814a3ef03985936a858

README.md

@@ -91,14 +91,6 @@ uwsgi/snap/nova-placement-api.ini will no longer be used.
 The services for the nova snap will log to its $SNAP_COMMON writable area:
 /var/snap/nova/common/log.
 
-## Managing nova
-
-The nova snap has alias support that enables use of the well-known
-nova-manage command. To enable the alias, run the following prior to
-using the command:
-
-    sudo snap alias nova.manage nova-manage
-
 ## Restarting nova services
 
 To restart all nova services:

snapcraft.yaml

@@ -52,8 +52,6 @@ apps:
       - network
   manage:
     command: snap-openstack nova-manage
-    aliases:
-      - nova-manage
     plugs:
       - network
 parts: