Stepping always happens in Liftoff now, and always by byte offset. Thus
remove the redundant "wasm-stepping-byte-offset" test, which was fully
subsumed by "wasm-stepping-liftoff". Also, rename
"wasm-stepping-liftoff" to "wasm-stepping".

R=thibaudm@chromium.org

Bug: chromium:1137710
Change-Id: Ifb68ce795ecdcbb1f85500dc4be4c2e64d15a9c6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2474116Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70528}