Deprecated panel stride alignment in bli_config.h.

Details:
- Removed BLIS_CONTIG_STRIDE_ALIGN_SIZE from bli_config.h of all
  configurations. It was already going unused in packm_init() since the
  recent 4m/3m commit. This setting was rarely, if ever, useful, and its
  existence only posed a potential risk for 4m/3m-based implementations.
- Removed BLIS_CONTIG_STRIDE_ALIGN_SIZE usage from mem_pool_macro_defs.h.
- Updated comments regarding CONTIG_STRIDE_ALIGN_SIZE in template
  micro-kernels.