The Sixth Amendment does not provide grounds for overturning the conviction of a man who insisted on representing himself in his trial on bank robbery charges, a federal appeals court held.In a nonprecedential order Wednesday, the 7th U.S. Circuit Court of Appeals held the record shows that defendant Robert D. Abbott’s assertion of his right to proceed pro se “was knowing, voluntary, and unequivocal.”But the court acknowledged that U.S. District Judge Lynn Adelman of the Eastern District of Wisconsin …