[turbofan] Simplify and fix JS typed lowering type init.
[turbofan] Simplify and fix JS typed lowering type init.

Removing and fixing some embarrassing stuff in js-typed-lowering.

BUG=
R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/981533003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#26991}

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh