test_planner: move pruning-related methods to new source file

These methods are all related to removing test suites from the eventual
test plan.

This refactor will simplify changes for crbug.com/976530

BUG=chromium:976530
TEST=unit tests (generator_test.go covers this new file)

Change-Id: I3ba45b8ce116595a34faa7080a089ac13c522b59
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/test_planner/+/1673550
Reviewed-by: Jason Clinton <jclinton@chromium.org>
Commit-Queue: Sean Abraham <seanabraham@chromium.org>
Tested-by: Sean Abraham <seanabraham@chromium.org>
4 files changed
tree: d5c1ae85869dff35fb8e814e5767c2061c056d4a
  1. .gitignore
  2. LICENSE
  3. OWNERS
  4. cipd.yaml
  5. deploy_cipd.json
  6. deploy_cipd.sh
  7. src/