Revert "Require that all changes to VM have TEST line"

This reverts commit a2ceec3e25.

Reason for revert: presubmit hooks are run very early (before CL description is edited), which breaks common workflows.

Original change's description:
> Require that all changes to VM have TEST line
>
> All changes touching one of the following directories will after this
> change be required to contain TEST= line.
>
>     runtime/vm
>     runtime/bin
>     runtime/lib
>     runtime/include
>     runtime/observatory
>     runtime/observatory_2
>     runtime/platform
>     sdk/lib/_internal/vm
>     pkg/vm
>
> This line is supposed to describe in free form how change was validated,
> for example by listing existing or newly added tests.
>
> The goal behind this requirement is to remind both reviewer and change
> author that changes to the code base are in general expected to be
> covered by tests, especially when CL is addressing a regression which
> slipped through existing testing.
>
> Having TEST line in the description would allow both author and
> reviewer to take additional time to consider if validation was
> sufficient or additional test coverage is needed.
>
> The inspiration for this line comes from Chromium[1].
>
> [1] https://chromium.googlesource.com/chromiumos/docs/+/master/contributing.md#describe-testing-performed
>
> TEST=changed file in runtime/vm and run git cl presubmit
>
> Change-Id: Ie16cf7c14af18e3a22a17084c0aebb4d1dfd6d23
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/169640
> Commit-Queue: Vyacheslav Egorov <vegorov@google.com>
> Reviewed-by: Martin Kustermann <kustermann@google.com>
> Reviewed-by: Siva Annamalai <asiva@google.com>

TBR=vegorov@google.com,kustermann@google.com,asiva@google.com

Change-Id: Ib2e198c322447e8d1166d5d05b2f3209d168f1e9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/169887
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
Commit-Queue: Vyacheslav Egorov <vegorov@google.com>

PRESUBMIT.py

@@ -262,47 +262,6 @@ def _CheckLayering(input_api, output_api):
     return []
 
 
-def _CheckTestPlan(input_api, output_api):
-    """Run test plan check.
-
-  Each change that touches specified directories in the checkout are required
-  to have TEST= line explaining how this change was validated.
-  """
-
-    DIRS = [
-        'runtime/vm',
-        'runtime/bin',
-        'runtime/lib',
-        'runtime/include',
-        'runtime/observatory',
-        'runtime/observatory_2',
-        'runtime/platform',
-        'pkg/vm',
-        'sdk/lib/_internal/vm',
-    ]
-
-    # Run only if directory was affected.
-    files = [f.LocalPath() for f in input_api.AffectedFiles()]
-    affected = filter(lambda dir: any(f.startswith(dir) for f in files), DIRS)
-    if len(affected) != 0 and input_api.change.tags.get('TEST', '') == '':
-        return [
-            output_api.PresubmitError('Change is missing TEST= line',
-                                      long_text="""
-When changing files in one of the following directories you
-must include TEST= line at the end of your change description.
-
-    %s
-
-This line is expected to explain in a free form the kind of testing
-that was performed to validate effect of the change. For example,
-it can list newly added tests or already existing tests which are assumed
-to cover the change.
-""" % ('    '.join(affected)))
-        ]
-
-    return []
-
-
 def _CheckClangTidy(input_api, output_api):
     """Run clang-tidy on VM changes."""
 
@@ -374,7 +333,6 @@ def _CommonChecks(input_api, output_api):
     results.extend(_CheckLayering(input_api, output_api))
     results.extend(_CheckClangTidy(input_api, output_api))
     results.extend(_CheckTestMatrixValid(input_api, output_api))
-    results.extend(_CheckTestPlan(input_api, output_api))
     results.extend(
         input_api.canned_checks.CheckPatchFormatted(input_api, output_api))
     return results