CLEANUP: http-ana: Remove useless if statement about L7 retries

CLEANUP: http-ana: Remove useless if statement about L7 retries

Thanks to the commit 1f08bffe0 ("MINOR: http-ana: Perform L7 retries because
of status codes in response analyser"), the L7 retries about the response
status code is now fully handled in the HTTP response analyser.
CF_READ_ERROR flag is no longer set on the response channel in this
case. Thus it is useless to try to catch L7 retries when CF_READ_ERROR is
set because it cannot happen.

The above commit was backported to 2.4, thus this one should also be
backported.