misc: Remove if (timer_pending) stop_timer idiom from the code

osmo_timer_del is an idempotent operation. There is no requirement
to check if it is running. If you don't want a timer to run, delete
it. Maybe one should have called the method _unschedule, _cancel to
make this more clear.
diff --git a/src/sysmo_sock.cpp b/src/sysmo_sock.cpp
index a4cc6de..d4fb5a6 100644
--- a/src/sysmo_sock.cpp
+++ b/src/sysmo_sock.cpp
@@ -304,8 +304,7 @@
 	if (!state)
 		return;
 
-	if (osmo_timer_pending(&state->timer))
-		osmo_timer_del(&state->timer);
+	osmo_timer_del(&state->timer);
 
 	bfd = &state->conn_bfd;
 	if (bfd->fd > 0)