Make AuctionProcessManager::LaunchProcess() not take ProcessHandles.

It only needs a couple fields inside a ProcessHandle, and doesn't set
the process associated with the Handle, so best to pass in only the
fields it needs. This also lets us not create a ProcessHandle when not
needed.

Bug: None
Change-Id: I0057c83305ca8cfd3a76b1241dfa717b73eef99a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5933667
Reviewed-by: Abigail Katcoff <abigailkatcoff@chromium.org>
Commit-Queue: mmenke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1369019}