We have reassigned a number of our contributions to one single contribution page - as the source was good enough for our record keeping purposes.
You cannot delete this Contribution Page because it has already been used to submit a contribution or membership payment. It is recommended that your disable the page instead of deleting it, to preserve the integrity of your contribution records. If you do want to completely delete this contribution page, you first need to search for and delete all of the contribution transactions associated with this page in CiviContribute.
The page no longer has contributions associated with it. Even test ones - I searched for them all - no memberships were ever processed via that page either.