Refactor slide sub-generator
Remove unnecessary option

This is the default anyway...
Refactor slide sub-generator test case

Finally no more Yeoman output during test runs. `npm test` no yields

```bash
> coffeelint app/index.coffee slide/index.coffee test Gruntfile.coffee

  ✓ app/index.coffee
  ✓ slide/index.coffee
  ✓ test/test-app-file-creation.coffee
  ✓ test/test-load.coffee
  ✓ test/test-slide-file-creation.coffee
  ✓ Gruntfile.coffee

✓ Ok! » 0 errors and 0 warnings in 6 files

  Generator Reveal
    ✓ generates package.json with correct version (79ms)
    ✓ updates .yo-rc.json config according to prompt input (46ms)
    ✓ generates SASS support for themes (47ms)
    ✓ generates Build control configuration for Github Pages Deployment
    ✓ uses selected theme when not using sass (39ms)
    with defaults
      ✓ should generate dotfiles
      ✓ generates expected boilerplate files
      ✓ uses defaults for .yo-rc.json config

  Generator Reveal
    ✓ can be imported without blowing up

  Sub-Generator Slide
    ✓ can be imported without blowing up

  Sub-Generator Slide
    default (no options passed)
      ✓ creates html slide
    with --attributes option
      ✓ creates html slide with attributes hash in list.json
    with --notes option
      ✓ creates html slide with notes
    with --markdown and --notes options
      ✓ creates markdown slide with notes
    with --markdown option
      ✓ creates markdown slide
    with --markdown and --attributes options
      ✓ creates markdown slide with attributes hash in list.json

  16 passing (522ms)
```