travis: remove the hack to build the Windows job on Azure Pipelines

travis: remove the hack to build the Windows job on Azure Pipelines

Since Travis did not support Windows (and now only supports very limited
Windows jobs, too limited for our use, the test suite would time out
*all* the time), we added a hack where a Travis job would trigger an
Azure Pipeline (which back then was still called VSTS Build), wait for
it to finish (or time out), and download the log (if available).

Needless to say that it was a horrible hack, necessitated by a bad
situation.

Nowadays, however, we have Azure Pipelines support, and do not need that
hack anymore. So let's retire it.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>