After fixing resp.filters, resp.do_esi loses its meaning.

Note:

Setting resp.filters also fixes whether or not the gunzip and range VDPs
are being pushed.

These do not depend on switches, but on request headers. So we need to
consider the case that a VCL author

	- fixes resp.filters
	- and then adds or removes relevant headers

* req.http.Accept-Encoding for the gunzip vdp

  if removed: gunzip stays in the VDP list, which is always ok

  if added: that is probably wrong anyway and the VCL author can
  be held responsible for their actions as per the warning in the
  resp.filters documentation.

* req.http.Range for the range vdp

  if removed: the range vdp vetoes itself in the _init callback

  if added: no range handling will be present, which is always ok
  (and see above for VCL author responsibilities)

Fixes #3002