Unused / irrelevant functions in the launch config builder

[eyalroz]

We have a static function named cuda::grid::detail_::validate_all_dimension_compatibility in the launch config builder class' header file - and we don't use it anywhere. Looking more closely, there is a somewhat-related function, launch_config_builder_t::resolve_dimensions() - which sets the overall dimensions based on the grid and block dims; and that's something we don't even need to do.

Now, within the get_composite_dimension() method, it would be appropriate to perform this validation - so that we don't arbitrarily choose to abide by two of the three specified dimensions, ignoring the third; and that current doesn't happen. Also, since that's the only place the validation is relevant - we can probably let go of the whole function.