Removing definition of _CRT_SECURE_NO_WARNINGS.

WebRTC code compiles with //build/config/compiler:chromium_code, which
adds "/wd4996" and makes _CRT_SECURE_NO_WARNINGS redundant.

Bug: None
Change-Id: If033e7c60cc1a640db77d075aab07b2562740d4a
Reviewed-on: https://webrtc-review.googlesource.com/72001
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22991}
diff --git a/BUILD.gn b/BUILD.gn
index 1c3d55d..99e2006 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -139,10 +139,7 @@
     defines += [ "WEBRTC_FUCHSIA" ]
   }
   if (is_win) {
-    defines += [
-      "WEBRTC_WIN",
-      "_CRT_SECURE_NO_WARNINGS",  # Suppress warnings about _vsnprinf
-    ]
+    defines += [ "WEBRTC_WIN" ]
   }
   if (is_android) {
     defines += [