linker: remove references to no longer exist _k_memory_pool

Commit 73cb9586ce0645b8d7634d6454a69349e718bc20 renamed linker
section from _k_memory_pool to _k_mem_pool, but the references
in linker scripts are still there. So remove them now.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>
2 files changed