You don't need to report anything about an unused EIN on your tax return.
(You may, however, want to close your account if you are getting a lot of mail from the IRS)
From the IRS website:
The IRS cannot cancel your EIN. Once an EIN has been assigned to a business entity, it becomes the permanent Federal taxpayer identification number for that entity. Regardless of whether the EIN is ever used to file Federal tax returns, the EIN is never reused or reassigned to another business entity. The EIN will still belong to the business entity and can be used at a later date, should the need arise.If you receive an EIN but later determine you do not need the number (the new business never started up, for example), the IRS can close your business account.
To close your business account, send us a letter that includes the complete legal name of the entity, the EIN, the business address and the reason you wish to close your account. If you have a copy of the EIN Assignment Notice that was issued when your EIN was assigned, include that when you write to us at:
Internal Revenue Service
Cincinnati, Ohio 45999
