Revert of [Telemetry] Update the code that detect windows version to use CurrentMajorVersionNumber

telemetry/telemetry/internal/platform/win_platform_backend.py

Index: telemetry/telemetry/internal/platform/win_platform_backend.py
diff --git a/telemetry/telemetry/internal/platform/win_platform_backend.py b/telemetry/telemetry/internal/platform/win_platform_backend.py
index 58240665afac910fc7fb264d38523de24c00348f..d43689276b55bdc5ef8e90d00709e518aa63d50d 100644
--- a/telemetry/telemetry/internal/platform/win_platform_backend.py
+++ b/telemetry/telemetry/internal/platform/win_platform_backend.py
@@ -36,10 +36,6 @@
   import win32gui  # pylint: disable=import-error
   import win32pipe  # pylint: disable=import-error
   import win32process  # pylint: disable=import-error
-  try:
-    import winreg  # pylint: disable=import-error
-  except ImportError:
-    import _winreg as winreg  # pylint: disable=import-error
   import win32security  # pylint: disable=import-error
 except ImportError:
   pywintypes = None
@@ -52,7 +48,6 @@
   win32pipe = None
   win32process = None
   win32security = None
-  winreg = None
 
 
 def _InstallWinRing0():
@@ -243,22 +238,12 @@
       return os_version_module.VISTA
     if os_version.startswith('6.1.'):
       return os_version_module.WIN7
-    # The version of python.exe we commonly use (2.7) is only manifested as
-    # being compatible with Windows versions up to 8. Therefore Windows *lies*
-    # to python about the version number to keep it runnable on Windows 10.
-    key_name = r'Software\Microsoft\Windows NT\CurrentVersion'
-    key = winreg.OpenKey(winreg.HKEY_LOCAL_MACHINE, key_name)
-    value, _ = winreg.QueryValueEx(key, 'CurrentMajorVersionNumber')
-    key.Close()
-    if value == 10:
+    if os_version.startswith('6.2.'):
+      return os_version_module.WIN8
+    if os_version.startswith('10.'):
       return os_version_module.WIN10
-    elif os_version.startswith('6.2.'):
-      return os_version_module.WIN8
-    elif os_version.startswith('6.3.'):
-      return os_version_module.WIN81
-    raise NotImplementedError(
-        'Unknown win version: %s, CurrentMajorVersionNumber: %s' %
-        (os_version, value))
+
+    raise NotImplementedError('Unknown win version %s.' % os_version)
 
   def CanFlushIndividualFilesFromSystemCache(self):
     return True