Revert "domain_conf: check device address before attach"

Revert "domain_conf: check device address before attach"

This reverts commit f1d6585300001c7b23b8796a0faa4411c3531996.

Turns out, this caused a regression. There is this (perhaps less
known) semantic of virDomainAttachDevice() where if the device
the API is trying to attach is a CDROM/floppy that is already in
the domain the attach request is handled as 'change the media in
the drive'.

We have a better fix anyways.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Tested-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Jim Fehlig <jfehlig@suse.com>