vtc: Reduce the window size in r3159

It was increased in 635f9f20 to avoid
sanitizer suppressions to scroll out of screen the lines we expect to
find, but on some 32bit ARM system it makes the test even less stable.

bin/varnishtest/tests/r03159.vtc

@@ -10,7 +10,7 @@ shell {
 	EOF
 }
 
-process p1 -winsz 200 80 -log {
+process p1 -winsz 100 80 -log {
 	varnishd -F -n "${tmpdir}/t" -a "${tmpdir}/sock" \
 	    -p vcc_err_unref=off -f "${tmpdir}/unref.vcl" 2>&1
 } -start