sh: Remove racy test case for read builtin.

This test case sometimes fails because of an EINTR-related race condition.
Fixing this race condition likely requires an extra system call per byte,
which would make the read builtin even slower than it already is, or very
complicated trickery. Therefore, remove the test case for now.

tools/regression/bin/sh/builtins/read8.0

@@ -1,13 +0,0 @@
-# $FreeBSD$
-
-T=`mktemp -d ${TMPDIR:-/tmp}/sh-test.XXXXXX`
-trap 'rm -rf $T' 0
-cd $T || exit 3
-mkfifo fifo1
-trapped=
-trap trapped=1 QUIT
-{ kill -QUIT $$; sleep 1; exit 4; } >fifo1 &
-read dummy <fifo1
-r=$?
-kill $!
-[ "$r" -gt 128 ] && [ -n "$trapped" ]