Revert "Sync readline/ to version 7.0 alpha"

Revert "Sync readline/ to version 7.0 alpha"

This reverts commit b558ff043d41ba8d17a82f5f9ae5f9dade66160e.
This reverts commit 4a11f2065906976675808364ddbd1c0f77eea41f.

The initial import commit failed to retain local changes made to
readline's configure.in (and the commit message erroneously stated that
there were no local changes that needed to be reapplied).  Also the
import caused a couple of build errors and a scattering of testsuite
regressions throughout many arches.  It's probably better to start over
with this import, hopefully more carefully next time.