contrib: remove "mw-to-git"

The "mw-to-git" directory contains tools for accessing MediaWiki via
Git. The scripts are essentially unmaintained in Git: despite a couple
of global cleanups, the last changes were a couple of security-related
issues part of 9a86064 (remote-mediawiki: use "sh" to eliminate
unquoted commands, 2020-09-21) and its parents. We don't ever run any of
the tests so it is more likely than not that many of the tests have been
bitrotting, like e.g. documented in f8ab018 (remote-mediawiki tests:
annotate failing tests, 2020-09-21).

According to Matthieu Moy [1], one of the original developers of this
tool, it didn't receive any attention recently and there is no
motivation to keep maintaining it anymore in the community. The project
has been spun out of Git [2] and thus has a new official home, but did
not receive much attention over there, either.

As such, it seems like the MediaWiki transport helper is slowly fading
away. But given that there is a new home, it doesn't make sense to have
it as part of Git anymore only to let it rot. Remove the directory.

[1]: <[email protected]>
[2]: https://github.com/Git-Mediawiki/Git-Mediawiki

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t