lib/libbl[ao]cklist: Use LIB_PACKAGE

This avoids e.g. utilities or ssh depending on the full blocklist
package just because they link against libblocklist.

This change moves files between packages so, until we have a proper
policy on how to handle this in release/stable branches, it should
not be MFC'd.

MFC after: never
Reviewed by: bapt
Sponsored by: https://www.patreon.com/bsdivy
Differential Revision: https://reviews.freebsd.org/D53605