In addition to the obvious formatting change, this also drops
from deps.go any indirect dependencies, so that when you add
a new import to one package, the resulting diff only affects that
one package, not every package that imports that package
directly or indirectly. That makes the file a bit easier to understand,
if you need to debug it or deal with a possible merge conflict.

The code to trim the import lists (but not too much) was more
than I wanted to do in shell, so I rewrote mkdeps in Go.

The shell script is left behind for backwards-compatibility with
people who have learned to run ./mkdeps.bash (or documentation
suggesting the same).

Change-Id: I0bf27b5b27d0440e11ea830b00735c73f58eae03
Reviewed-on: https://go-review.googlesource.com/67650Reviewed-by: David Crawshaw <crawshaw@golang.org>