[Fuchsia] Remove unused services from test sandbox CMX fragment.

Since we currently run all test suites in a "headless" environment, and
use the Ozone "headless" platform for tests which need Ozone, we don't
(and can't) have tests make use of Scenic nor Vulkan services.

Removing these services from the sandbox ensures that no dependencies
on them creep in to our test suites, which is important since
requesting a service provided by Scenic may actually cause Scenic to
be (re)launched, potentially leading to hard to diagnose flakiness.

Bug: DX-1801
Change-Id: Id26fa23664d4b693dab8514ae8957229432c6034
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1716339
Commit-Queue: Wez <wez@chromium.org>
Auto-Submit: Wez <wez@chromium.org>
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Michael Spang <spang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682132}

build/config/fuchsia/tests.cmx

@@ -31,9 +31,6 @@
       "fuchsia.sysmem.Allocator",
       "fuchsia.ui.input.ImeService",
       "fuchsia.ui.input.ImeVisibilityService",
-      "fuchsia.ui.policy.Presenter",
-      "fuchsia.ui.scenic.Scenic",
-      "fuchsia.vulkan.loader.Loader",
       "fuchsia.web.ContextProvider"
     ]
   }