sysutils/screen: Make MULTIUSER default
Setuid root screen uses /tmp/screen for its sockets while non-setuid root
screen uses /tmp/uscreens. This is too much of a POLA violation, therefore
make MULTUSER default. This commit reverts the intent of PR/262903. People
wishing to secure their screen must terminate all screen sessions before
rebuilding without the MULTIUSER option.
Reported by: many
Fixes: 2022Q2