Details:
- Removed explicit reference to The University of Texas at Austin in the
  third clause of the license comment blocks of all relevant files and
  replaced it with a more all-encompassing "copyright holder(s)".
- Removed duplicate words ("derived") from a few kernels' license
  comment blocks.
- Homogenized license comment block in kernels/zen/3/bli_gemm_small.c
  with format of all other comment blocks.