treewide: kernel: drop redundant USB_EHCI_HCD=n config symbol
Commit e53ec043bae1 ("kirkwood: move usb support to modules") has moved
this config symbol into generic configs, so it could be removed from
other configs.
Suggested-by: Aleksander Jan Bajkowski <[email protected]>
Signed-off-by: Petr Štetiar <[email protected]>