Revert "serial: 8250_exar: Fill in rs485_supported"

This reverts commit 9ef7419b which is
commit 59c221f8 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I9e062adb35dc7fe9c71ae48f20d0936552b10e48
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>