stop passing default '-k' QEMU option from datacenter.cfg

stop passing default '-k' QEMU option from datacenter.cfg

Modern noVNC does not needs this anymore, actually things may get
worse if it's used. E.g., when one sets 'de' and the VM locale is
'de' you may get a 'ĸ' (unicode kra) if you want to send an ampersand
character through pressing SHIFT + 6.

Qemus manual pages confirms that this is most times not needed
anymore:

 > -k language
 >    Use keyboard layout language (for example "fr" for
 >    French). This option is only needed where it is not
 >    easy to get raw PC keycodes (e.g. on Macs, with some
 >    X11 servers or with a VNC or curses display). You don't
 >    normally need to use it on PC/Linux or PC/Windows
 >    hosts.
 -- man kvm

An user can always set it per VM, wew simply remove the implict
default derived from the cluster wide datacenter.cfg

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>