exchange 2007 Public Folder Database cannot be deleted

We are in the process of decommissioning exchange 2007 server from 2007 <-> 2013 coexistence.

All user MailboxDatabases have been sucsessfully removed, however PF Mailbox databases return an error. “The public folder database 'Public Folder Database' cannot be deleted”

Object is read only because it was created by a future version of Exchange: 0.10 (14.0.100.0). Current supported version is 0.1 (8.0.535.0).

I am suspecting the presence for 2 OAB is the reason why we can’t delete Public folder database from 2007 server.

Get-OfflineAddressBook on 2007 returns

Name               Server             Versions           AddressLists

----               ------             --------           ------------

Default Offline ... ex07                {Version4}          {\Default Global...

Default Offline ... Offline Address ... {Version4}         {\Default Global...

Get-OfflineAddressBook on 2013 returns

Name                                   Versions                               AddressLists

----                                   --------                               ------------

Default Offline Address Book           {Version4}                             {\Default Global Address List}

Default Offline Address Book (Ex2012)  {Version4}                             {\Default Global Address List}

Questions:

1. How can I check if both exchange servers are still OAB generation servers?
2. I am not sure if the previous service provider moved OAB,  can I potentially cause any problems by executing  

Get-MailboxDatabase | Set-MailboxDatabase -OfflineAddressBook "\Default Offline Address Book (Ex2013)"

Move-OfflineAddressBook -Identity "Default Offline Address Book" -Server EX13

  3. Is it safe to delete 2007 OAB ?

Thanks