Revert of Add a presubmit check that warns about declaring Singleton<T> in header files

PRESUBMIT.py

Index: PRESUBMIT.py
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 3000e106c00767b00167cb87c75949090b725a6c..18fe621e4f5524f6156c5e93f5982f4d227d9e7b 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -1303,36 +1303,6 @@
     sys.path = original_sys_path
 
   return copyright_scanner.ScanAtPresubmit(input_api, output_api)
-
-
-def _CheckSingletonInHeaders(input_api, output_api):
-  """Checks to make sure no header files have |Singleton<|."""
-  def FileFilter(affected_file):
-    # It's ok for base/memory/singleton.h to have |Singleton<|.
-    black_list = (_EXCLUDED_PATHS +
-                  input_api.DEFAULT_BLACK_LIST +
-                  (r"^base[\\\/]memory[\\\/]singleton\.h$",))
-    return input_api.FilterSourceFile(affected_file, black_list=black_list)
-
-  pattern = input_api.re.compile(r'(?<!class\s)Singleton\s*<')
-  files = []
-  for f in input_api.AffectedSourceFiles(FileFilter):
-    if (f.LocalPath().endswith('.h') or f.LocalPath().endswith('.hxx') or
-        f.LocalPath().endswith('.hpp') or f.LocalPath().endswith('.inl')):
-      contents = input_api.ReadFile(f.LocalPath())
-      for line in contents.splitlines(False):
-        if (not input_api.re.match(r'//', line) and # Strip C++ comment.
-            pattern.search(line)):
-          files.append(f)
-          break
-
-  if files:
-    return [ output_api.PresubmitError(
-        'Found Singleton<T> in the following header files.\n' +
-        'Please move them to an appropriate source file so that the ' +
-        'template gets instantiated in a single compilation unit.',
-        files) ]
-  return []
 
 
 _DEPRECATED_CSS = [
@@ -1452,7 +1422,6 @@
   results.extend(_CheckForIPCRules(input_api, output_api))
   results.extend(_CheckForCopyrightedCode(input_api, output_api))
   results.extend(_CheckForWindowsLineEndings(input_api, output_api))
-  results.extend(_CheckSingletonInHeaders(input_api, output_api))
 
   if any('PRESUBMIT.py' == f.LocalPath() for f in input_api.AffectedFiles()):
     results.extend(input_api.canned_checks.RunUnitTestsInDirectory(