Avoid rescheduling HostDBContinuation to the ET_DNS thread.
Avoid rescheduling HostDBContinuation to the ET_DNS thread.

With TS-196 (commit a5345da8), the HostDBContinuation is no longer
reschedule to the ET_DNS. However, the changes only applied to the
`HostDBProcessor::getbyname_imm` interface.

And the NCA feature was removed by TS-455 (commit 112b03aa), so it is
safe to bring the changes to all the interfaces of HostDBProcessor.

SolidWallOfCode/trafficserver,duke8253/trafficserver,dyrock/trafficserver,SolidWallOfCode/trafficserver,dyrock/trafficserver,pbchou/trafficserver,duke8253/trafficserver,vmamidi/trafficserver,chitianhao/trafficserver,pbchou/trafficserver,duke8253/trafficserver,SolidWallOfCode/trafficserver,SolidWallOfCode/trafficserver,chitianhao/trafficserver,pbchou/trafficserver,chitianhao/trafficserver,davidbz/trafficserver,bryancall/trafficserver,pbchou/trafficserver,vmamidi/trafficserver,pbchou/trafficserver,duke8253/trafficserver,dyrock/trafficserver,SolidWallOfCode/trafficserver,chitianhao/trafficserver,vmamidi/trafficserver,duke8253/trafficserver,dyrock/trafficserver,chitianhao/trafficserver,chitianhao/trafficserver,vmamidi/trafficserver,chitianhao/trafficserver,davidbz/trafficserver,bryancall/trafficserver,bryancall/trafficserver,SolidWallOfCode/trafficserver,dyrock/trafficserver,bryancall/trafficserver,vmamidi/trafficserver,davidbz/trafficserver,bryancall/trafficserver,bryancall/trafficserver,dyrock/trafficserver,SolidWallOfCode/trafficserver,duke8253/trafficserver,davidbz/trafficserver,dyrock/trafficserver,vmamidi/trafficserver,davidbz/trafficserver,davidbz/trafficserver,duke8253/trafficserver,pbchou/trafficserver