ike: Don't reset optional CHILD_SA properties when migrating child-creating tasks

These are set via methods, which are not called again after migration
(e.g. when retrying due to INVALID_KE or when moving queued tasks), so we
don't want to clear these values.

src/libcharon/sa/ikev1/tasks/quick_mode.c

@@ -1475,7 +1475,6 @@ METHOD(task_t, migrate, void,
 	this->dh = NULL;
 	this->spi_i = 0;
 	this->spi_r = 0;
-	this->child = (child_sa_create_t){};
 
 	if (!this->initiator)
 	{

src/libcharon/sa/ikev2/tasks/child_create.c

@@ -1876,7 +1876,6 @@ METHOD(task_t, migrate, void,
 	this->ipcomp_received = IPCOMP_NONE;
 	this->other_cpi = 0;
 	this->established = FALSE;
-	this->child = (child_sa_create_t){};
 }
 
 METHOD(task_t, destroy, void,