On all platform, the method is implemented identical to
{LoadInstanceFromFrame}. So remove {FillInstanceInto} and keep
{LoadInstanceFromFrame} which is a better name.

R=thibaudm@chromium.org

Bug: v8:12425
Change-Id: Ia9e6a3e2478628f8d31ff4faaab8d5250fda7796
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3429203Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78924}