Don't crash when running InlineEditorProvider tests on the mac

The avoids the crash when running the InlineEditorProvider tests on the mac (bug #4328). Rather than deleting the temp directory after _every_ spec, delete it once at the end of the suite. 

Prior to adobe/brackets-shell#265, `SpecRunnerUtils.deletePath(..)` didn't do anything if you passed in a directory. Now it deletes the directory immediately.