core: axe data_in_in/output_filter from conn_rec.

They were superseded by ap_filter_should_yield() and ap_run_in/output_pending()
in r1706669 and had poor semantics since then (we can't maintain pending
semantics both by filter and for the whole connection).

Register ap_filter_input_pending() as the default input_pending hook (which
seems to have been forgotten in the first place).

On the MPM event side, we don't need to flush pending output data when the
connection has just been processed, ap_filter_should_yield() is lightweight and
enough to determine whether we should really enter write completion state or go
straight to reading. ap_run_output_pending() is used only when write completion
is in place and needs to be completed before more processing.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1836364 13f79535-47bb-0310-9956-ffa450edef68