Revert "serial: Add rs485_supported to uart_port"

This reverts commit dfd8b9d2 which is
commit 8925c31c 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: I4e137aa48fb787f1600c7133d62f4a273f22fbf9
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>