MAINTAINERS: Remove defunct iss storage mailing list

It appears that the mailing list email address doesn't exist anymore:

<iss_storagedev@hp.com>: host smtp.hp.com[15.73.96.116] said: 550 5.1.1
    <iss_storagedev@hp.com>: Recipient address rejected: User unknown in
    virtual alias table (in reply to RCPT TO command)

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Acked-by: Don Brace <don.brace@microsemi.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>