Update rfc/wip-tform/index.md

rm zarr2 specific phrasing

Co-authored-by: Davis Bennett <[email protected]>

rfc/wip-tform/index.md

@@ -110,7 +110,7 @@ the last dimension of an array in "C" order are stored contiguously on disk or i
 
 
 The name and axes names MAY be customized by including a `arrayCoordinateSystem` field in
-the `.zattr` metadata of the array whose value is a coordinate system object. The length of
+the user-defined attributes of the array whose value is a coordinate system object. The length of
 `axes` MUST be equal to the dimensionality. The value of `"type"` for each object in the 
 axes array MUST equal `"array"`.