Maintainer list housekeeping

[Jon Turney]

> Aaron Schneider is a maintainer, but has no key
> Yitzchak Scott-Thoennes is a maintainer, but has no key
> Yue Ren is a maintainer, but has no key

These package maintainers have no recorded ssh public key, which means 
they haven't uploaded a package using the current package upload system, 
which has been in use since October 2013.

The relevant lines from cygwin-pkg-maint:

> 4ti2                                         Yue Ren/Marco Atzeri
> cddlib                                       Yue Ren/Marco Atzeri
> flint                                        Yue Ren/Marco Atzeri
> fortune-mod                                  Yitzchak Scott-Thoennes
> ntl                                          Yue Ren/Marco Atzeri
> pv                                           Aaron Schneider
> singular                                     Yue Ren/Marco Atzeri
> surf                                         Yue Ren/Marco Atzeri

Marco,

Can you tell me if Yue Ren is still active, or if his maintainership 
should be dropped?

I propose to orphan the other packages.