cmd/go/testdata/script: stop using network from mod_git_export_subst

The export-subst vcstest git repo adds the necessary parts of
github.com/jasonkeene/export-subst that were used in the test earlier.

For #80243

Change-Id: I9cf1bc0fb304ac5cbbd9ce49605a44e16a6a6964
Reviewed-on: https://go-review.googlesource.com/c/go/+/795903
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Michael Matloob <matloob@google.com>

src/cmd/go/testdata/script/mod_git_export_subst.txt

diff --git a/src/cmd/go/testdata/script/mod_git_export_subst.txt b/src/cmd/go/testdata/script/mod_git_export_subst.txt
index 740ccbdb..c8b5988 100644
--- a/src/cmd/go/testdata/script/mod_git_export_subst.txt
+++ b/src/cmd/go/testdata/script/mod_git_export_subst.txt
@@ -1,21 +1,21 @@
-env GO111MODULE=on
 env GOPROXY=direct
+env GONOSUMDB=vcs-test.golang.org
 
 # Testing that git export-subst is disabled
-[!net:github.com] skip
+[short] skip 'uses git'
 [!git] skip
 go build
 
 -- x.go --
 package x
 
-import _ "github.com/jasonkeene/export-subst"
+import _ "vcs-test.golang.org/git/export-subst.git"
 
 -- go.mod --
 module x
 
-require github.com/jasonkeene/export-subst v0.0.0-20180927204031-5845945ec626
+require vcs-test.golang.org/git/export-subst.git v0.0.0-20180927204031-98817ac105fc
 
 -- go.sum --
-github.com/jasonkeene/export-subst v0.0.0-20180927204031-5845945ec626 h1:AUkXi/xFnm7lH2pgtvVkGb7buRn1ywFHw+xDpZ29Rz0=
-github.com/jasonkeene/export-subst v0.0.0-20180927204031-5845945ec626/go.mod h1:DwJXqVtrgrQkv3Giuf2Jh4YyubVe7y41S1eOIaysTJw=
+vcs-test.golang.org/git/export-subst.git v0.0.0-20180927204031-98817ac105fc h1:JSFJzPmCTsz2eFs1jjb40Tun7DZZ6TZQUWgsh8VNZYE=
+vcs-test.golang.org/git/export-subst.git v0.0.0-20180927204031-98817ac105fc/go.mod h1:UgzsJqCUIrlpaTSm+IYkSmrpeo+9g12tsw/rNKnMfwE=

src/cmd/go/testdata/vcstest/git/export-subst.txt

diff --git a/src/cmd/go/testdata/vcstest/git/export-subst.txt b/src/cmd/go/testdata/vcstest/git/export-subst.txt
new file mode 100644
index 0000000..47ecb1d
--- /dev/null
+++ b/src/cmd/go/testdata/vcstest/git/export-subst.txt
@@ -0,0 +1,23 @@
+handle git
+
+env GIT_AUTHOR_NAME='Gopher'
+env GIT_AUTHOR_EMAIL='gopher@golang.org'
+env GIT_COMMITTER_NAME=$GIT_AUTHOR_NAME
+env GIT_COMMITTER_EMAIL=$GIT_AUTHOR_EMAIL
+
+git init
+
+at 2018-09-27T20:40:31+00:00
+
+git add .gitattributes go.mod export_subst.go
+git commit -m 'initial commit'
+git branch -m master
+
+-- .gitattributes --
+export_subst.go export-subst
+-- go.mod --
+module vcs-test.golang.org/git/export-subst.git
+-- export_subst.go --
+package export_subst
+
+const CommitHash = "$Format:%H$"