This CL reverts the runtime lowering introduced here -
https://codereview.chromium.org/1991143002/
Additional ops to the runtime pass will cause GC issues as WASM frames may
have outgoing arguments to runtime calls that have pointers that aren't scanned.

Preserving decoding of SIMD opcodes and macros for native implementations.

R=bbudge@chromium.org, mtrofin@chromium.org, bradnelson@chromium.org

Review-Url: https://codereview.chromium.org/2235013002
Cr-Commit-Position: refs/heads/master@{#38564}