This reverts commit 6233b088.

Conflicts:
	bin/varnishd/cache/cache_req.c

The conflict was introduced with the handling of h2 stream 0 pseudo
request: 51127b46. This fixes a
regression where timeout_idle could be circumvented by a periodic
CRLF, except that it has no real consequence like holding onto a
worker thread thanks to timeout_linger kicking in as expected.

In addition to reverting the change, test coverage is added.