Remove SCREEN_LOGDIR from devstack

SCREEN_LOGDIR has already been deprecated [1]
[1] https://review.openstack.org/#/c/499186

Change-Id: Ia27a87ef5dfc02ff888a17e5078450e7b71905d1

install.sh

@@ -37,9 +37,6 @@ function err() {
     set +o xtrace
     local msg="[ERROR] ${BASH_SOURCE[2]}:$1 $2"
     echo $msg 1>&2;
-    if [[ -n ${SCREEN_LOGDIR} ]]; then
-        echo $msg >> "${SCREEN_LOGDIR}/error.log"
-    fi
     $errXTRACE
     return $exitcode
 }