[Extensions] Update StartupHelperBrowserTests to manifest v2

StartupHelperBrowserTests have been updated to manifest v2.
Remove the allowance for manifest v1 extensions.

Bug: 816679
Change-Id: Ib11500da4e22cd74f60193e5fd3d3c0368fb686f
Reviewed-on: https://chromium-review.googlesource.com/1024600
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553863}
1 file changed