I believe this part has seen very little change from the Revised
Haskell 98 Report.
I was in fact looking at the Haskell 98 report at the time.
It is not clear that it is an unintended leftover. Section 2.1 that
Nothing is ever clear. This useless pedanticism being stipulated, there is no purpose to a completely overlapping category unless it is intended to relate to an earlier standard (say Haskell 1.4).
Unicode support is clearly intended. Also clearly, ASCII support is intended.
However, the Report does not say what the concrete syntax of a Unicode character
should be. (At least I have been unable to find it from the report.)
Maybe what needs to be pedantically specified is that the link to the Unicode standard is intended to be inclusion of that standard by reference (the [11] in the section I quoted is an endnote referencing the Unicode standard) and not merely informational. Or are you insisting we are not precise enough unless we enumerate all the Unicode characters explicitly in the Haskell standard?