lib/geom: remove redundant libraries and objects

Do not link lib/geom/raid with libmd, it is not required for the module.
Do not include the sha256/sha512 code in lib/geom/eli, it is provided by
libmd. Remove ${.CURDIR:H:H}/misc from .PATH for all modules. This
path has stopped being valid when the GEOM modules were moved from
sbin/geom to lib/geom.

Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D47061