source_test_config: remove source_tree field

This field is no longer populated or used by config or by the test
planner. We use the file_patterns field instead now.

BUG=chromium:1007377
TEST=regen

Change-Id: I46ce38fd14438485592dcd3419a4099857bd560c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/proto/+/1837334
Tested-by: Sean Abraham <seanabraham@chromium.org>
Auto-Submit: Sean Abraham <seanabraham@chromium.org>
Reviewed-by: David Burger <dburger@chromium.org>
Commit-Queue: Sean Abraham <seanabraham@chromium.org>
5 files changed