The webdriver patch deleted navigator.webdriver, leaving it `undefined`. Real
Chrome reports `false`, so `undefined` is itself a detection tell, and deleting
it also removes the native `false` that Emulation.setAutomationOverride sets.
Now we rely on setAutomationOverride for a native (undetectable) `false` and
only force `false` via a getter as a fallback when webdriver is still `true`
(older Chrome without that override) — never delete it. Verified: FullLaunch
headless now reports navigator.webdriver === false (boolean), consistently.