Band-aid fix for local([@%]$x)

Band-aid fix for local([@%]$x)

This fixes the segfaults by extending the prohibition on `local($$x)'
to array and hash dereferences and removing the code that never
worked. It also adds simple test cases and a `through' to the error
message.

The new explanation in perldiag isn't terribly clear, but the old one
told an untruth.

It should be possible to make local([$@%]$x) work by adding a new
SAVEt type, and I'd like to do so in the future, but that certainly
wouldn't be maintenance patch material.

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