This reverts commit e44fdc70.

Reason for revert: Breaks msan:
https://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20arm64%20-%20sim%20-%20MSAN/builds/17482

Original change's description:
> [wasm] [multival] Allow function types as block types
> 
> Changes the binary encoding of multi-return blocks to contain a function type index instead of a vector of value types.
> 
> Cf. https://github.com/WebAssembly/multi-value/blob/master/proposals/multi-value/Overview.md#binary-format
> 
> Bug: v8:6672
> Change-Id: I506d9323bfd6dba1e7a24c8590bcf5a08b68c433
> Reviewed-on: https://chromium-review.googlesource.com/599807
> Reviewed-by: Ben Titzer <titzer@chromium.org>
> Commit-Queue: Andreas Rossberg <rossberg@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#48453}

TBR=titzer@chromium.org,rossberg@chromium.org

Change-Id: Ia711d16ec6bd1c0731a96d38b8661f05be71f64b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:6672
Reviewed-on: https://chromium-review.googlesource.com/712634Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48455}