In the first case, the only thing they will notice (perhaps not) is that they slipped from first level connection to second level connection with you. Here are instructions to remove a connection.
In skill endorsements, there is no way for someone to see that you eliminated their endorsement of you, unless they look at every endorser for that skill and notice they are no longer on that list. Here are instructions to remove a skills endorsement.
And if you want to rescind an endorsement that you gave someone else, here’s how.
Now you know.