Remove the concept of IC age from the heap and SFI, since it no
longer does anything useful.

Change-Id: I4ce466efc77c007c09c0889bae09ec6a0c907e33
Reviewed-on: https://chromium-review.googlesource.com/593623
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47041}