Revert "Replace variadic_function.h with variadic templates."

This reverts commit f91e7e1bee9f68e4ef9ce49878647f85ed94a133.

Change-Id: Id75e54fc86b4c54ffb85d6f0cc3546e418a2be81
Reviewed-on: https://code-review.googlesource.com/4820
Reviewed-by: Paul Wankadia <junyer@google.com>
5 files changed