conveyor_pose: set explicit assignment operator for CustomICP

Since PCL 1.12 the assignment operator of IterativeClosestPoint has been set to delete
which causes an implicit deletion of the inheriting class CustomICP.
Refer to PointCloudLibrary/pcl#4167 for further
details.

src/plugins/conveyor_pose/recognition_thread.h

@@ -40,6 +40,11 @@
 class CustomICP : public pcl::IterativeClosestPointNonLinear<pcl::PointXYZ, pcl::PointXYZ>
 {
 public:
+	CustomICP &
+	operator=(CustomICP other)
+	{
+		return *this;
+	}
 	using pcl::IterativeClosestPointNonLinear<pcl::PointXYZ,
 	                                          pcl::PointXYZ>::IterativeClosestPointNonLinear;