Revert "serial: 8250_exar: Fill in rs485_supported"

This reverts commit 84bf7b87 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: Iba320d6a91720f36a89029762c28133427af93dd
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>