ci: rm `test-sdk` job from submodule_update.yml

The approach to build SDK since 3.0 release series is changed and will
be under development for some period of time. So the `test-sdk` job is
just irrelevant now and expected to fail. Let's remove the job until it
is clear how to implement the integration testing in the scope of the
new approach for SDK build.

NO_DOC=ci
NO_TEST=ci
NO_CHANGELOG=ci