This patch removes support for the `assert` keyword
for import attributes. It was an old variant of the
proposal that was only shipped in V8 and no other
engine, and that has then been replaced by the `with`
keyword.

Chrome is planning to remove support for `assert`
in version 126, which will be released in June.

Node.js already supports the `with` keyword for
import attributes, and this patch does not change that.