Remove CUBE profiling from xGPU

[maddyscientist]

There is no need as far as I can see to maintain CUBE in the xGPU library. CUBE was introduced as an automated profiling utility for xGPU since when xGPU was written the CUDA profiler was immature. Since then, the profiler has significantly advanced and can give much more detailed and useful information for CUBE. Moreover, the simple flops counting mechanism of CUBE is not required since the operation count is trivial.

The continued presence of CUBE in the library just obfuscates further development. I am therefore going to remove it, simplifying the code base.