File robots.txt needed in Craft package?
The specific directive to disallow the /craft/ directory isn't necessary if your craft folder is below the webroot.

However, it's good practice to have a robots.txt for each site, so I don't recommend deleting it altogether. You can change the directives to fit whatever robots criteria you need for your site. (For example, if you launch a beta site, you'd want to Disallow the whole thing to avoid duplicate content penalties.)