runtime: remove __go_alloc and __go_free

Move allocg and handling of allgs slice from C to Go.

Change-Id: I579aa6dfc09e9e635106e9d36c4e3ab0bce6fa7a
Reviewed-on: https://go-review.googlesource.com/34797
Reviewed-by: Than McIntosh <thanm@google.com>
18 files changed