This is a first step to removing the support for the OldFunctions
section altogether, which will greatly simplify the encoder and remove
the need to do local variable remapping in asm->wasm.

R=bradnelson@chromium.org,aseemgarg@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/1974933002
Cr-Commit-Position: refs/heads/master@{#36228}