ge_bx50v3: Remove unused USB related defines

These USB defines do not change the build as there is no USB support
enabled currently.

Cc: Ian Ray <ian.ray@ge.com>
Cc: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>