Remove support for pre v16 joi

[kanongil]

The last joi@15.1.1 was released more than 4 years ago. It should be safe to drop (in a breaking release).

This also removes several npm deprecation notices when installing dev dependencies.

[damusix]

@kanongil Is this still a valid PR? Any chance you can update it if need be? We're converging for a major release and may include this if it's ready.

[kanongil]

There might be an issue with this PR, let me check…

[kanongil]

We need to keep support for non-async validators, since an external validator might only use this.

Ie. I have removed the logic changes, and this patch just replaces the legacy joi test, with a custom non-async validator test.

The test failures seem unrelated to this PR. Note that node@14 also a fails while reporting a false positive.

[kanongil]

Note that since this no longer changes the logic, this patch could also be applied against the main branch.

[damusix]

@kanongil Can you rebase and fix the lint errors on this?

[kanongil]

No – It is already based of the tip of next. I have made a new PR against master, though.