Revert "serial: Add rs485_supported to uart_port"

This reverts commit 87c81c19 which is
commit 8925c31c upstream.

It breaks the kernel API and is not needed for any Android devices, so
revert it for now.  If it is needed in the future, it can be brought
back in an ABI-safe way.

Bug: 161946584
Change-Id: I67ec53c5baa5f85f180c81abbf5035b0303587aa
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>