Due to a recent refactoring the function EnsureEventLoopInitialized on
the default platform became obsolete. It does not contain a single line
of code. With this CL we prepare the removal of this function from the
V8 platform API.

R=rmcilroy@chromium.org

Bug: v8:7310
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng;master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: If4d54cd989f8df2f40b322be3b67bb8a482398d0
Reviewed-on: https://chromium-review.googlesource.com/934221
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51635}