fix(test): remove redundant nested afterEach in Reset test causing Windows hang

fix(test): remove redundant nested afterEach in Reset test causing Windows hang

The Reset test had nested describes (B11, B12) with their own afterEach
calling standardCleanup(), plus an outer afterEach calling mock.timers.reset()
then standardCleanup(). This caused mock.restoreAll() to be called twice
per test with timer reset in between - leaving MockTracker in inconsistent
state on Windows.

Also harmonize StationHelpers cleanup to use '= undefined' consistently
instead of mixing with 'delete'.