[Fuchsia] Remove unused 'launchpad' include path.
[Fuchsia] Remove unused 'launchpad' include path.

We've already migrated to the new fdio_spawn*() API, and no longer use
launchpad.

Change-Id: Ieaba20eba2a1b9281429bfa7f4d564f8b167964a
Reviewed-on: https://chromium-review.googlesource.com/1143715
Reviewed-by: Mark Mentovai <f1b5a91d4d6ad523f2610114591c007e75d15084@chromium.org>

chromium/mini_chromium,chromium/mini_chromium,chromium/mini_chromium