Now that darwin/arm no longer use an explicit -p=1 in the go command
remove the explicit -p=<num cpus> from gomobile as well.
While we're here, fix the init test templates to reflect the new
clang based build.
Fixesgolang/go#10477
Change-Id: I29a179e628466ae0c591620f485194b80e310811
Reviewed-on: https://go-review.googlesource.com/21186
Reviewed-by: David Crawshaw <crawshaw@golang.org>