Revert of services/shell: Turn on sandboxing for mojo apps. (patchset #9...

Revert of services/shell: Turn on sandboxing for mojo apps. (patchset #9 id:180001 of https://codereview.chromium.org/2338793003/ )

Reason for revert:
Causes a timeout on mash_browser_tests.

Original issue's description:
> services/shell: Turn on sandboxing for mojo apps.
>
> Turn on sandbox for mojo apps by default. Apps that need to run
> without a sandbox need to include 'shell:unsandboxed' in their
> capabilities in manifest for mojo:shell.
>
> Update manifests for mojo:ui, mojo:font_service, mojo:file_system,
> and mojo:leveldb services to include 'shell:unsandboxed'.
>
> BUG=645602, 646376
>
> Committed: https://crrev.com/43aa4f706d6020c93f11fa952d7f1d7a7337c570
> Cr-Commit-Position: refs/heads/master@{#419891}

TBR=rockot@chromium.org,ben@chromium.org,tsepez@chromium.org,sadrul@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=645602, 646376

Review-Url: https://codereview.chromium.org/2353783004
Cr-Commit-Position: refs/heads/master@{#419928}