ps(1): clean up after swapout removal
The process flag P_INMEM is always set. Eliminate all checks for the
bit. Also eliminate LAZY_PS define and code covered by it: we do not
have an u-area for long time, and it cannot be swapped out.
Also eliminate setting controlled by the '-f' switch, but accept it for
backward compatibility.
The 'W' process secondary state (swapped out) is impossible, stop
calculating it.
Reviewed by: markj
Sponsored by: The FreeBSD Foundation
Differential revision: https://reviews.freebsd.org/D47492