It's actually mandated by the FAA that an ashtray be present in the restrooms:

> (g) Regardless of whether smoking is allowed in any other part of the airplane, lavatories must have self-contained, removable ashtrays located conspicuously on or near the entry side of each lavatory door, except that one ashtray may serve more than one lavatory door if the ashtray can be seen readily from the cabin side of each lavatory served.

And the plane literally cannot fly with an inoperable or missing ashtray.