Revert of Change default Windows compiler to VS 2015

build/vs_toolchain.py

Index: build/vs_toolchain.py
diff --git a/build/vs_toolchain.py b/build/vs_toolchain.py
index bb3e853d686317c87c68367fcd258e9f816037bf..f6aef3aeab04a90b5b7bc072098c9eff0d7b61ee 100755
--- a/build/vs_toolchain.py
+++ b/build/vs_toolchain.py
@@ -21,8 +21,8 @@
 import gyp
 
 
-# Use MSVS2015 as the default toolchain.
-CURRENT_DEFAULT_TOOLCHAIN_VERSION = '2015'
+# Use MSVS2013 as the default toolchain.
+CURRENT_DEFAULT_TOOLCHAIN_VERSION = '2013'
 
 
 def SetEnvironmentAndGetRuntimeDllDirs():
@@ -274,6 +274,7 @@
     # Update 1 with Debuggers, UCRT installers and ucrtbased.dll
     return ['523b6c2d3df300b2c8538cdc0beac404726af051']
   else:
+    # Default to VS2013.
     return ['4087e065abebdca6dbd0caca2910c6718d2ec67f']
 
 
@@ -307,9 +308,6 @@
         depot_tools_win_toolchain):
     import find_depot_tools
     depot_tools_path = find_depot_tools.add_depot_tools_to_path()
-    # Necessary so that get_toolchain_if_necessary.py will put the VS toolkit
-    # in the correct directory.
-    os.environ['GYP_MSVS_VERSION'] = GetVisualStudioVersion()
     get_toolchain_args = [
         sys.executable,
         os.path.join(depot_tools_path,