[gin] Use new command line feature for Wasm inlining

https://crrev.com/c/4335553 added --experimental-wasm-inlining as the
new source of truth for enabling Wasm inlining.
Hence the finch trial should use that flag. We can then remove the
previous (now redundant) --wasm-inlining and --wasm-speculative-inlining
flags.

R=leszeks@chromium.org
CC=jkummerow@chromium.org

Bug: 1424350
Change-Id: I518165ac9dd92bb1e89e9a32ce96d060326817ae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4344272
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1119279}