Reland "[fuchsia] Remove use of ambient VMEX capabilities"

This is a second reland of
commit 32d1466c6def9112df62366e9d9872b282ba1f25, after addressing
security policy & routing issues up-stream.

- Remove job_policy_ambient_mark_vmo_exec from all component
  manifests.
- Remove most usage of the ambient-VMEX-capable ELF test runner.

Some use of the ambient-VMEX ELF runner remains, to support tests
which run SwiftShader in-process, which requires ambient-VMEX for its
shader JIT.

The test CML fragment for the VMEX-capable ELF test runner is also
still required by out-of-tree dependencies, notably ANGLE.

Bug: 1290907, 1185811, 1022542
Change-Id: I7bd4308469abf350ee8ea48a1e6371bc2f11284c
Cq-Include-Trybots: luci.chrome.try:fuchsia-smoke-astro,fuchsia-smoke-sherlock
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4626516
Owners-Override: Wez <wez@chromium.org>
Reviewed-by: David Dorwin <ddorwin@chromium.org>
Commit-Queue: David Dorwin <ddorwin@chromium.org>
Auto-Submit: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1161336}