Remove some unrequired dependencies between jobs in Gitlab CI

• Remove unittest_hooks -> builds_hooks_* dependencies.

It is not required. Just as there is no dependency for unittest_backend -> core build_* jobs. There is no reason to require extra checks on hooks vs core.

• Remove unittest_backend -> unittest_hooks dependency.

Both pass most of the time. No need to try to save up time in the case the first one fails. And it is still beneficial to have results on both.

• Remove danger -> deploy_demo dependency.