Revert of [x64] Zero/sign-extend loads to 64-bit registers. (patchset #1 id:20001 of https://codereview.chromium.org/2220483003/ )

Reason for revert:
Breaks tree:
https://build.chromium.org/p/client.v8/builders/V8%20Linux64%20-%20debug/builds/10969

Original issue's description:
> [x64] Zero/sign-extend loads to 64-bit registers.
>
> Before this change we would first load an 8/16/32-bit value from memory into a 32-bit register, then zero/sign-extend from that register to a 64-bit one. Now we replace that pattern with a single movsx/movzx.
>
> Ported from http://crrev.com/2183923003
>
> R=bmeurer@chromium.org
>
> Committed: https://crrev.com/4abecb7a27bd5fa073d0ff5fadb0c2bb248ef9f4
> Cr-Commit-Position: refs/heads/master@{#38388}

TBR=bmeurer@chromium.org,epertoso@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review-Url: https://codereview.chromium.org/2221473002
Cr-Commit-Position: refs/heads/master@{#38389}