docs/system/deprecated: Fix note on fdc drive properties

docs/system/deprecated: Fix note on fdc drive properties

Commit 4a27a638e7 "fdc: Deprecate configuring floppies with -global
isa-fdc" actually deprecated any use of floppy controller driver
properties, not just with -global.  Correct the deprecation note
accordingly.

Fixes: 4a27a638e718b445648de6b27c709353551d9b44
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-id: 20210309161214.1402527-2-armbru@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>