Remove $FreeBSD$: one-line sh pattern

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

Migrate tools/regression/usr.bin/pkill to the new tests layout.

Interestingly, the pkill tool lives in bin, not usr.bin. Haven't bothered
to check if this is because the tool moved or because the tests were
originally added in the wrong place.