cad/systemc: match RESTRICTED text with /usr/ports/LEGAL

The former maintainer indicates that he no longer has time to work on
this port. He understands is not staged and thus headed for removal,
so the RESTRICTED update is being done by itself in case somebody else
steps up to stage the port.

PR: 189883
Submitted by: maintainer (at the time) (Daniel Thiele)
Approved by: portmgr (implicit, NOT_STAGED)