docs: smbios: remove family=x from type2 entry description

'family' option is not part of type 2 table and if user tries to use it
as such QEMU will error out with an unknow option error.
Drop it from docs lest it confuse users.

Fixes: b155eb1d04 ("smbios: document cmdline options for smbios type 2-4, 17 structures")
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <1558448611-315074-1-git-send-email-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

qemu-options.hx

@@ -2080,7 +2080,7 @@ Specify SMBIOS type 0 fields
 @item -smbios type=1[,manufacturer=@var{str}][,product=@var{str}][,version=@var{str}][,serial=@var{str}][,uuid=@var{uuid}][,sku=@var{str}][,family=@var{str}]
 Specify SMBIOS type 1 fields
 
-@item -smbios type=2[,manufacturer=@var{str}][,product=@var{str}][,version=@var{str}][,serial=@var{str}][,asset=@var{str}][,location=@var{str}][,family=@var{str}]
+@item -smbios type=2[,manufacturer=@var{str}][,product=@var{str}][,version=@var{str}][,serial=@var{str}][,asset=@var{str}][,location=@var{str}]
 Specify SMBIOS type 2 fields
 
 @item -smbios type=3[,manufacturer=@var{str}][,version=@var{str}][,serial=@var{str}][,asset=@var{str}][,sku=@var{str}]