Previously, the taskmgr, timermgr and socketmgr had a constructor
variant, that would create the mgr on top of existing appctx. This was
no longer true and isc_<*>mgr was just calling isc_<*>mgr_create()
directly without any extra code.
This commit just cleans up the extra function.
"resolve" is used by the resolver system tests, and I'm not
certain whether delv exercises the same code, so rather than
remove it, I moved it to bin/tests/system.
