USB: more pxa2xx_udc dead code removal

Remove some more dead code from the pxa2xx_udc driver:  support
for a no-longer-undocumented hardware "test mode".  Newer chips
made this the default, evidently as the best workaround for deep
silicon bugs.  The interest was that this seemed to be the only
way to kick in the (documented!) double buffering capability.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>