Rework BGP timers to work with channel

Since netty channel gives us scheduling capabilities, there is simply no
need for an external timer.  So let's get rid of it and simplify our
code.

Change-Id: If6b7f84dbb953fc1766a6ddceb8411abcf1dc442
Signed-off-by: Robert Varga <rovarga@cisco.com>
Signed-off-by: Dana Kutenicsova <dkutenic@cisco.com>
Merge "Rework BGP timers to work with channel"