Some Joomla 2.5.x core components (Banners, Contacts, Newsfeeds, Smart Search, and Weblinks) can be deleted via the Back-end: Extensions > Extension Manager > Manage > (select + delete)
Core component installation packages don't exist because it's too much work to maintain, and Joomla 2.5 has a nice feature called "discover".
Note: The following method is recommended:
- upload the contents of a Joomla full package (without /installation/ directory) to your website
- use Extensions > Extension Manager > Discover to discover & install uninstalled extensions.
- The components table structures + the component reference in #__extensions + the component menu items will all be created automatically.
- The component reference in #__assets will not be created using "discover": to recreate, use Components > [component name] > [Options] (icon in upper right corner) > Permissions (tab) > [save & close]