Before AppEngine classic allowed "google.golang.org/appengine" imports,
we used to maintain two hook files to choose either from "appengine" or
"google.golang.org/appengine" namespaces. Now, both environments allow
importing from "google.golang.org/appengine". Therefore, there
is no need to set hooks in two separate files.
Also note that Flex prefers to use metadata server, so we still
need to be able to differentiate between these environments.
Change-Id: I7478ebdfa1b062d466aaf2aca938f93d42b4c58a
Reviewed-on: https://go-review.googlesource.com/37378
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>