devel/rhtvision: fix build on FreeBSD 15.1

The header <termios.h> needs to be included in unixkey.cc for this
port to build. I presume it got previously included transitively
but now isn't anymore.

While we are at it, define LICENSE and have the port not run
ldconfig at stage time.

MFH: 2026Q2
(cherry picked from commit 2b39263be5a6d1a4d6cd8e8162e40f18776e220c)