bsdinstall: Drop vestigial bsdinstall-esps cleanup

This is not needed after 0b7472b3d8d2f1e90fade5236b44fd98d8e396c2.

MFC after: 3 days
Sponsored by: iXsystems, Inc.
Reviewed by: imp
Differential Revision: https://reviews.freebsd.org/D29325

(cherry picked from commit b07b7aec6534052d60cffe010c0426a7ab986d85)