ginkgo: Remove K8sDatapathCustomCalls

[ upstream commit 0da3f7e ]

Currently, the feature is not used, and its test is blocking the LVH
upgrade [1][2]. Let's remove the test case. Once it is in use, we should
rethink the testing approach (either implement as a BPF unit test, or
an advanced CLI connectivity test).

[1]: #27599
[2]: #27688

Backporting conflicts:
* .github/actions/ginkgo/main-focus.yaml doesn't exist in v1.13

Signed-off-by: Martynas Pumputis <m@lambda.lt>
Signed-off-by: Gilberto Bertin <jibi@cilium.io>