You can prevent these paths from being generated in the first place - there's a setting in the admin:
System > Configuration > Catalog > Catalog > Use Categories Path for Product URLs:
Set this to No. A reindex of
core_url_rewrite table should remove any unwanted urls.
Warning: This will remove all of the category names from all URLs, leaving only the base URL key. There's no way that I'm aware of to perform the opposite - provide only the deepest-depth URL as the canonical URL.
Magento creates these 'pages' by default in the site root and in all relevant categories to provide logical directory structure of product pages within any category as well as standalone pages in the site root.
My suggestion: leave them enabled.
Having descriptive URLs to If you're concerned about duplicate content, you shouldn't be. You should instead enable the setting to display canonical meta tags - this will notify search engines which of the multiple pages you consider to be the de-facto standard page, which all other duplicate product pages are based on.
Below the option as displayed above in the admin is the option to enable canonicals.