Polling job for MediaWiki doxygen

There is no need to install MediaWiki, simply touching LocalSettings.php
is enough.

Doxygen stdout/stderr are captured on the host (user: jenkins-deploy)
then copied to the build dir for published. That requires /log/build to
be created before.

The git scm does not use reference repository, JJB support for it is
broken.

Jenkins filters outs unannotated tags since the sha1 got already build
via the matching branch. Hence we will no more generate Doxygen
documentation for each of the tags. I don't think it ever mattered.

Drop the legacy jobs that ran on Nodepool instances.

Bug: T115755
Change-Id: I495eb580bc350aa08c957d329907923a526d3100