vty: Remove command for manual channel activation/deactivation
vty: Remove command for manual channel activation/deactivation

OsmoBTS won't run without being connected to a BSC.  The BTS wouldn't
start to transmit if the BSC doesn't properly initialize it.  So if we
want to activate some channels manually for testing, we should do so
from the BSC, and not inside the BTS code.  Doing this in the BTS means
that the BSC is not aware of it and might want to use that channel for
something else meanwhile.

Osmo{BSC,NITB} has gained ability to manually activate a channel from
the VTY in Change-Id I44fc3904678eb48bd3ab1a3da8c0c265fa082e0d as can be
seen at https://gerrit.osmocom.org/2759

So let's remove the old/obsoleted code here.

Change-Id: I7ba0301b55cc283aa6a441899f84357e28a97321

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts