Remove force_win64 from the GN files; it's not needed anymore.
Remove force_win64 from the GN files; it's not needed anymore.

R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/738053004

chinmaygarde/mojo,chinmaygarde/mojo,afandria/mojo,collinjackson/mojo,jianglu/mojo,collinjackson/mojo,afandria/mojo,chinmaygarde/mojo,jianglu/mojo,chinmaygarde/mojo,jianglu/mojo,jianglu/mojo,collinjackson/mojo,jianglu/mojo,afandria/mojo,collinjackson/mojo,collinjackson/mojo,afandria/mojo,afandria/mojo,jianglu/mojo,collinjackson/mojo,afandria/mojo,chinmaygarde/mojo,collinjackson/mojo,chinmaygarde/mojo,collinjackson/mojo,afandria/mojo,jianglu/mojo,chinmaygarde/mojo,chinmaygarde/mojo,chinmaygarde/mojo,collinjackson/mojo,afandria/mojo,jianglu/mojo