Remove inappropriate array index error on slice copy

[dkorpel]

#12871 (comment)

Reverts back to an uninformative "Range Error". Slice copy was completely overlooked in dlang/druntime#3517, new druntime support has to be added before it can be improved again.

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[ibuclaw]

OK, thanks.

[Geod24]

@dlang-bot , asleep at the wheel again.