Revert 260949 "Move gtest/gmock BUILD.gn files to main tree."

> Move gtest/gmock BUILD.gn files to main tree.
> 
> Also moves the "unused variable warning" to a config in the build directory so
> it can be shared with outher targets without duplication on the command line.
> 
> BUG=
> R=cjhopman@chromium.org
> 
> Review URL: https://codereview.chromium.org/219433005

TBR=brettw@chromium.org

Review URL: https://codereview.chromium.org/218493017

git-svn-id: http://src.chromium.org/svn/trunk/src/build@260954 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

config/win/BUILD.gn

@@ -109,11 +109,3 @@ config("incremental_linking") {
 config("no_incremental_linking") {
   ldflags = [ "/INCREMENTAL:NO" ]
 }
-
-# Disable unused variable warning ----------------------------------------------
-
-# Sometimes third-party code wants to disable this warning under MSVC, so this
-# config makes it easy to do so.
-config("disable_unused_variable_warning") {
-  cflags = [ "/wd4800" ]
-}