msm: ipc: Cleanup a routing table entry under subsystem restart

Currently when a remote subsystem restarts, the routing table entry
corresponding to that remote subsystem is recycled. This causes some
subsystems to be not reachable if the system's network topology is
not meshed.

Remove the routing table entry for a restarting subsystem so that
it gets added again either through HELLO message from that subsystem or
through first NEW_SERVER message from that subsystem.

Change-Id: I2957ebfb2b66610f68e000e42e2c07d463c89eb6
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>