adv_monitor: Issue Remove Adv Monitor mgmt call

adv_monitor: Issue Remove Adv Monitor mgmt call

This calls Remove Adv Monitor command to kernel and handles the callback
during a monitor removal initiated by a D-Bus client. This also
registers callback for getting notified on Adv Monitor Removed event, so
that the Adv monitor manager can invalidate the monitor by calling
Release() on its proxy.

The following tests were performed.
- In bluetoothctl console, add a monitor and remove the monitor by its
index and verify the removal in both the output of btmgmt and syslog.
- In bluetoothctl console, add a monitor, remove the monitor via
btmgmt and verify the removal in syslog.

Change-Id: Ib51b9e6ce76e816e66bb7248e48be7364ca9812e
Signed-off-by: Anuj Jain <anuj01.jain@samsung.com>
Signed-off-by: Ayush Garg <ayush.garg@samsung.com>