Reland "NUX Onboarding: clean up build process."

The original CL 1252906 was reverted due to breaking unit tests for
branded window builds.

This CL fixes that by removing obsolete unit tests. It was testing the
mechanism that conditionally directs users to the chrome://welcome/email
and chrome://welcome/apps experiment URLs, which will no longer be used.

Bug: 874153
Change-Id: I3b92b53e191606a6f5889cf17b15a570ce566994
Reviewed-on: https://chromium-review.googlesource.com/c/1275294
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Scott Chen <scottchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599070}
19 files changed