Remove docs and tests for Charmcraft `simple` profile

[dwilding]

In Charmcraft 4.0, we're planning to remove the simple profile of charmcraft init (see https://github.com/canonical/charmcraft/pull/2295). When this is released, we'll need to change Ops:

• Change the note in Create a repository and initialise it to say that kubernetes is the default profile. Remove simple.

• Update charmcraft-profile-tests in published-charms-tests.yaml to stop testing simple.