Update libedit to a snapshot from 2019-09-10

This version bring many fixes regarding unicode support
It also adds proper support for filename completion (we do not need our custom
patches anymore)
Improves the libreadline compatibility

Note that the same work was done by Yuichiro Naito in
https://reviews.freebsd.org/D21196 the main difference is in this case we have
reimported libedit in contrib to fix a long standing mess in the previous merges
which prevented a proper update workflow. (discussed long ago with pfg@)

The only difference with upstream libedit is we have added a compatibility shim
for the _elf_fn_sh_complete function which we previously added to support quoting
in filename completion and is not needed anymore.
This was added to continue supported old /bin/sh binaries and not break backward
compatibility (as discussed with jilles@)

Reviewed by: Yuichiro Naito <naito.yuichiro_gmail.com>
MFC after: 3 weeks
Differential Revision: https://reviews.freebsd.org/D21584