generator: remove "disable non Tast" code path

I replaced this in config with a test group usage that does the same
thing, but doesn't require special coding like this did.
https://crrev.com/i/3284216

Also fix up some uses of vars in generator_test. These were previously
being altered by one test and inadvertently being used in that altered
form by other tests. I noticed this when I went to remove the non-Tast
test, only to find that the test wasn't failing when it should've been.
This tweak makes the tests properly independent again.

Bug: 1130018
Change-Id: I189b39031671dce61071a0c12cfdbeb792b26785
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/go/+/2425244
Tested-by: Sean Abraham <seanabraham@chromium.org>
Auto-Submit: Sean Abraham <seanabraham@chromium.org>
Reviewed-by: David Burger <dburger@chromium.org>
Commit-Queue: David Burger <dburger@chromium.org>
3 files changed