fix manifest warnings in versions.context.ui

[WARNING] bundle localization file
/home/hudson/.hudson/jobs/mylyn-reviews-snapshot/workspace/tbr/org.eclipse.mylyn.versions.context.ui/plugin.properties
not found
[WARNING] Bundle-Vendor header not found in
/home/hudson/.hudson/jobs/mylyn-reviews-snapshot/workspace/tbr/org.eclipse.mylyn.versions.context.ui/META-INF/MANIFEST.MF,
fallback to 'unknown' for source bundle

Change-Id: Icee2e876a68a01051c85433f2828c3855511ab5c
remove gerrit-2.9.1-dev fixture

Change-Id: If142d78fadd73252208b1fe0a7b8d8e4cf35846d