This is a cleanup to remove unneeded flags after these changes (in
https://crrev.com/c/1988548):
* --future does not imply --wasm-tier-up any more, and
* --wasm-tier-up does not imply --liftoff any more.

Instead, now
* --wasm-tier-up is enabled by default,
* --wasm-tier-up has no effect if --liftoff is not set, and
* --future implies --liftoff.

R=ahaas@chromium.org

Bug: chromium:1040061
Change-Id: I5d04ee1f1d84ddcd0654df0e0a4c6298f80aee9e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1993280Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65666}