Remove the regress test for the server's session keyring

Also stop installing keyutils in CI, which was only needed by the test.

.github/workflows/regress.yml

@@ -51,7 +51,6 @@ jobs:
             automake \
             bison \
             build-essential \
-            keyutils \
             libevent-dev \
             libncurses-dev \
             libutf8proc-dev \

regress/session-keyring.sh

@@ -1,71 +0,0 @@
-#!/bin/sh
-
-# On Linux the server should join a session keyring of its own, so it keeps
-# working after the login session's keyring is revoked, and revoke it when it
-# exits.
-
-PATH=/bin:/usr/bin
-TERM=screen
-
-[ "$(uname)" = Linux ] || exit 0
-keyctl session - true >/dev/null 2>&1 || exit 0
-
-[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
-OUT=$(mktemp -d)
-TMUX="$TEST_TMUX -Ltest$$ -f/dev/null"
-$TMUX kill-server 2>/dev/null
-
-fail()
-{
-	echo "$*"
-	exit 1
-}
-
-cleanup()
-{
-	$TMUX kill-server 2>/dev/null
-	[ -s $OUT/holder ] && kill $(cat $OUT/holder) 2>/dev/null
-	rm -rf "$OUT"
-}
-trap cleanup 0 1 15
-
-# Start the server from a login session with its own keyring, then revoke that
-# keyring as pam_keyinit(8) does when the login session ends.
-LOGIN=$(keyctl session - sh -c "
-	$TMUX new -d 'sleep 1000' && keyctl id @s && keyctl revoke @s
-" 2>/dev/null) || fail "could not start server"
-
-# A new pane should still have a usable keyring, with the user keyring linked.
-$TMUX new-window -d "keyctl id @s >$OUT/pane 2>&1; $TMUX wait-for -S pane" ||
-	fail "could not create pane"
-$TMUX wait-for pane
-KEYRING=$(cat $OUT/pane)
-case "$KEYRING" in
-''|*[!0-9]*)
-	fail "pane keyring not usable: $KEYRING"
-	;;
-esac
-[ "$KEYRING" != "$LOGIN" ] || fail "pane has the login keyring"
-keyctl rlist $KEYRING | grep -qw "$(keyctl id @u)" ||
-	fail "user keyring not linked"
-
-# The server should revoke its keyring when it exits, even while a process it
-# started (which ignores the SIGHUP from its pane closing) still holds it.
-$TMUX new-window -d "
-	trap '' HUP
-	echo \$\$ >$OUT/holder
-	$TMUX wait-for -S held
-	exec sleep 100
-" || fail "could not create pane"
-$TMUX wait-for held
-SERVER=$($TMUX display -p '#{pid}')
-$TMUX kill-server
-n=0
-while kill -0 $SERVER 2>/dev/null && [ $n -lt 50 ]; do
-	sleep 0.1
-	n=$((n + 1))
-done
-keyctl rdescribe $KEYRING >$OUT/exit 2>&1
-grep -q "revoked" $OUT/exit || fail "keyring not revoked: $(cat $OUT/exit)"
-
-exit 0