buildsys: use QEMU's keycodemapdb again

buildsys: use QEMU's keycodemapdb again

instead of the split-out version that was last updated for QEMU 6.0.
This reverts the relevant part of 6838f03 ("bump version to 2.11.1-1")
which doesn't state a reason why the splitting was done. If something
breaks, we can still re-do it and document the reason this time.

Alternatively, it would be necessary to adapt the paths, because
keycodemapdb lives in subprojects/ rather than ui/ since QEMU commit
c53648abba ("meson: use subproject for keycodemapdb").

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>