They add up to a considerable chunk of the VSL traffic, especially when
cookies are involved, while providing little value when troubleshooting.
In an effort to reduce VSL cycles on heavy workloads I found these to be
good candidates for several reasons:

- obj.* fields are immutable in VCL
- after a hit, we initially get the same Resp* records in vcl_deliver
- before vcl_backend_response returns, we can infer them from Beresp*

The main difference would be ObjHeader:X-Varnish, but it would be the
same as BerespHeader:X-Varnish, and be part of the RespHeader counterpart
in the case of a hit. That, and cache-related headers adjusted to the
current time.

One case where they wouldn't appear is for example on a hit followed by
a restart. I have yet to find a use case where I'd need to query them
with varnishlog or some other VUT.