linux-raspberrypi: Drop local 5.10 recipes in favour of upstream

meta-raspberrypi now comes with this version already: 5.10. 5.10 in
oniro was an upgrade for dunfell but now that we move to newer layers,
we can drop it and use the latest in upstream.

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>