Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Deorbit catman. The tradeoff of disk for performance has long since tipped
in favor of just rendering the manpage instead of relying on pre-formatted
catpages. Note, this does not impede the ability to use existing catpages,
it just removes the utility to generate them.

Reviewed by: imp, allanjude
Approved by: emaste (mentor)
Differential Revision: https://reviews.freebsd.org/D12317

Fix installation of makewhatis.local(1) since r283777.

The wrapper script has moved to libexec/makewhatis.local since it is not
directlry related to the older makewhatis(1) utility that has been replaced
by the usr.bin/mandoc version.

Reported by: vangyzen