Revert of Default-enable external startup data for Linux for stand-alone...

Revert of Default-enable external startup data for Linux for stand-alone builds. (patchset #1 id:1 of https://codereview.chromium.org/959693002/)

Reason for revert:
Breaks "Simple Leaks Check"

Original issue's description:
> Default-enable external startup data for Linux for stand-alone builds.
>
> Notes:
> - Other platforms to follow later.
> - This follows Chromium practice, that mostly uses this feature these days.
> - The statically linked-in startup data will stay. So whoever prefers
>   the old way just needs to set the flag differently.
>
> BUG=
>
> Committed: https://crrev.com/6d0dcaabe55ca3556bebfd771fbc7fd560fdd4e0
> Cr-Commit-Position: refs/heads/master@{#26884}

TBR=machenbach@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/962593003

Cr-Commit-Position: refs/heads/master@{#26885}

build/standalone.gypi

@@ -151,11 +151,6 @@
       }, {
         'clang%': 0,
       }],
-      ['(OS=="linux")', {
-        # Gradually roll out v8_use_external_startup_data.
-        # Should eventually be default enabled on all platforms.
-        'v8_use_external_startup_data%': 1,
-      }],
     ],
     # Default ARM variable settings.
     'arm_version%': 'default',