Remove $FreeBSD$: one-line sh pattern

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

loader: install help files only once

Every file should be installed exactly once by `make installworld`.
This is especially important for pkgbase.

Loader help files were being installed by each loader variant (e.g.,
the simp, lua, and 4th EFI loaders). Add a (slightly hacky) mechanism
to skip installing help files for all but one variant.

PR: 271178
Reviewed by: imp
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D40021

Create a loader for each interpreter for x86 BIOS and all EFI

Create loader_{4th,lua,simp}{,.efi}. All of these are installed by
default. Create LOADER_DEFAULT_INTERP to specify the default
interpreter when no other is specified. LOADER_INTERP is the current
interpreter language building. Turn building of lua on by default to
match 4th. simploader is a simplified loader build w/o any interpreter
language (but with a simple loader). This is the historic behavir you
got with WITHOUT_FORTH. Make a hard link to the default loader. This
has to be a hard link rather than the more desirable soft link because
older zfsboot blocks don't support symlinks.

RelNotes: Yes
Differential Revision: https://reviews.freebsd.org/D16705