Use utilities from build directory instead of own copies

GYP and GN builds share some common utilities. GYP has three utilities
in its own directory which are also synced in build directory now.
We will use utilities from build directory instead of keeping our own
copies.

Compared to our own copies, utilities in build directory
are either same or newer.
find_depot_tools.py is identical;
vs_toolchain.py and find_sdk.py have some minor updates.

Review-Url: https://codereview.chromium.org/1933843002
diff --git a/DEPS b/DEPS
index 1a08ef3..0368c39 100644
--- a/DEPS
+++ b/DEPS
@@ -173,6 +173,6 @@
     # Update the Windows toolchain if necessary.
     'name': 'win_toolchain',
     'pattern': '.',
-    'action': ['python', 'pdfium/build_gyp/vs_toolchain.py', 'update'],
+    'action': ['python', 'pdfium/build/vs_toolchain.py', 'update'],
   },
 ]