Fix leaking temporary files when pylint is disabled

Test plan:
Crossed fingers
Start using parent linter lintFile implementation

The only pylint-specific functionality was the concept of 'enabled'. So we can
rely on the parent class to actually run pylint.

Test Plan:

  * Opened a window with pylint enabled, saw lint errors.
  * Opened a window with pylint disabled and saw no lint errors, but did see an
    error message in the console.