genomics: add an argument to provide the cache to kmers

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
Revert "genomics: add an argument to provide the cache to kmers"

This reverts commit 679cc2b975793a53769b2d222d72dbbc8a3a5dd7.

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>