Cleanup javascript build

Once vinz and storyboard have been migrated forward to use the
new JS build targets, we can remove the old build. This patch
removes the legacy gate-{name}-js-unittests target, and collapses
the explicit unit/integration/functional targets into one
configurable one (as per clarkb's comments on #106172).

Change-Id: I331fafdc70253a893027255128865d7239f1406e
Merge "Cleanup javascript build"