Remove unnecessary 'virtual' annotation from mojo

Removes virtual keyword from overridden methods in cpp_templates.

BUG=417463,469785
R=viettrungluu@chromium.org

Review URL: https://codereview.chromium.org/1037353002

Patch from Chris Greene <cwgreene@amazon.com>.
diff --git a/AUTHORS b/AUTHORS
index 34f6b48..2efca50 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -85,6 +85,7 @@
 Changjun Yang <changjun.yang@intel.com>
 Chansik Yun <chansik.yun@gmail.com>
 Chaobin Zhang <zhchbin@gmail.com>
+Chris Greene <cwgreene@amazon.com>
 Chris Harrelson <chrishtr@gmail.com>
 Christophe Dumez <ch.dumez@samsung.com>
 Christopher Dale <chrelad@gmail.com>