[OpenMP][libomptarget][AMDGPU] Update print launch info

Clean up for the AMD-specific kernel launch info in the NextGen Plugins.
- Fixes a mistake introduced with the initial commit that added printing
  of an AMD-only property.
- Removes another AMD-only property (not clear on upstream status)
- Adds some more comment to what info is printed.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D145924