Move browsertests from Wikibase.git into its own repository

Moved to https://github.com/wmde/WikidataBrowserTests

This should be merged together with this change for wdjenkins, which
changes the location the tests are pulled from:
https://github.com/wmde/jenkins-job-builder-config/pull/9

Bug: 66469
Change-Id: I6524a6d7e4d0993e8cd45a43854e137a8e075979
Merge "Move browsertests from Wikibase.git into its own repository"