* plugin/forward: remove dynamic read timeout

We care about an upstream being there, so we still have a dynamic dial
time out (by way higher then 200ms) of 1s; this should be fairly stable
for an upstream. The read timeout if more variable because of cached and
non cached responses. As such remove his logic entirely.

Drop to 2s read timeout.

Fixes #2306
Signed-off-by: Miek Gieben <miek@miek.nl>