Revert "cmd/go: use shallow clones for new git checkouts"

This reverts commit bc1f9d20.

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/16832Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/go/vcs.go

@@ -122,8 +122,8 @@ var vcsGit = &vcsCmd{
 	name: "Git",
 	cmd:  "git",
 
-	createCmd:   []string{"clone --depth=1 {repo} {dir}", "--git-dir={dir}/.git submodule update --init --recursive"},
-	downloadCmd: []string{"pull --depth=1 --ff-only", "submodule update --init --recursive"},
+	createCmd:   []string{"clone {repo} {dir}", "--git-dir={dir}/.git submodule update --init --recursive"},
+	downloadCmd: []string{"pull --ff-only", "submodule update --init --recursive"},
 
 	tagCmd: []tagCmd{
 		// tags/xxx matches a git tag named xxx