Convert gn_unittests to run exclusively on Swarming

0 configs already ran on Swarming
3 used to run locally and were converted:
- chromium.linux.json: Linux Tests
- chromium.linux.json: Linux Tests (dbg)(1)
- chromium.linux.json: Linux Tests (dbg)(1)(32)

Ran:
  ./manage.py --convert gn_unittests

BUG=98637

Review URL: https://codereview.chromium.org/1214533005

Cr-Commit-Position: refs/heads/master@{#336929}
3 files changed