Julien notes this is very likely unneeded:
!21 (diffs, comment 195929)

We had it like this since 01a01c8c (client: Add support for zodburi),
but I rechecked zodburi codebase now and it does not do any similar
lowering anywhere.

So drop support for case normalization in zurl options.

/cc @levin.zimmermann
/reviewed-by @jm
/reviewed-on !21