Revert "cmd/go: use shallow clones for new git checkouts"
This reverts commit
bc1f9d20b40998b87c9a5f56f2b22595de65c2d4.
The current go-get strategy doesn't support cases that servers
cannot handle shallow clients.
Also, `go get -u` is broken and is not compatible with already
go-getted unshallow repos.
Fixes #13213.
Fixes #13206.
Change-Id: Ie89d7603d96d323db64ad82997793fda0972f709
Reviewed-on: https://go-review.googlesource.com/16832
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>