Task #3114: Improve GPU update-constraints module
Add virtual site support to GPU version of update-constraints.
The virtual sites require forces to be distributed among normal atoms. Hence, all forces has to be copied to the host on every step if vsites are on. Since this defeats the purpose of offloading all computations to the device and introduces additional logical expressions into the main MD loop, the vsite support is removed. Consider moving force redistribution for virtual sites to the device so that no extra copy will be needed.