It appears that you did not load the client disk library. The error message states that it gapi.client.driveis undefined. You should have a line like:
gapi.client.load('drive', 'v2', function() { });
which will load the drive API and determine gapi.client.drive. Make sure you call delete in the callback, or else make sure it is driveloaded before attempting to delete the file.
, @MasNotsram, gapi.client.request delete.