… 'generic bounds in type aliases are ignored' warning

It is subsumed by ui/param-bounds-ignored.rs.

Also move the check for not having type parameters into ast_validation.

I was not sure what to do with compile-fail/issue-23046.rs: The issue looks like
maybe the bounds actually played a role in triggering the ICE, but that seems
unlikely given that the compiler seems to entirely ignore them.  However, I
couldn't find a testcase without the bounds, so I figured the best I could do is
to just remove the bounds and make sure at least that keeps working.