Those tell Install manager what has been installed and where - if you delete them the products will then appear in the Ready to Download or Ready to Install tab, depending on whether or not you kept the zips. Although there are a lot of files they are quite small - I am surprised they are filling your drive. Are you sure it isn't the Download folder that is taking up the space?

If you click the gear icon at top-right of the main Install Manager window to open Settings, you can set the locations used. The zips go to the Package Archive folder, set in the Downloads tab. The Manifests go to the Manifest Archive folder, set in the Installation tab. If you change the locations copy the contents of the old folder to the new.