Fix: sessiond: duplicated rotation notification sent

A duplicate notification that a rotation was launched and completed
is sent by the rotation thread when a rotation is performed after
a session was stopped.

This code is removed at it is a left-over from the time when the
rotation thread had to explicitly rename trace output folders
when a rotation had completed.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>