sysutils/exa: Mark deprecated

The project is abandoned upstream. It's been forked as eza,
and the fork already has a port, so recommend that instead.

PR: 298083
Reported by: asomers
Sponsored by: ConnectWise
Approved by: osa, vvd (Mentors, implicit)

(cherry picked from commit 20e6ca4c67147e14628de8bc47656bd7ee75f7c7)