Use auto-alias for keystone-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: I6ca747b83e8a930c9ba65cdfb36f8fc67609bd54

README.md

@@ -88,14 +88,6 @@ will no longer be used.
 The services for the keystone snap will log to its $SNAP_COMMON writable area:
 /var/snap/keystone/common/log.
 
-## Managing keystone
-
-The keystone snap has alias support that enables use of the well-known
-keystone-manage command. To enable the alias, run the following prior to
-using the command:
-
-    sudo snap alias keystone.manage keystone-manage
-
 ## Restarting keystone services
 
 To restart all keystone services:

snapcraft.yaml

@@ -22,8 +22,6 @@ apps:
       - network-bind
   manage:
     command: snap-openstack keystone-manage
-    aliases:
-      - keystone-manage
     plugs:
       - network