cmd/go: remove unused loader state

This test file does not make any use of the module loader state.

This commit is part of the overall effort to eliminate global
modloader state.

Change-Id: I198c76aef9d9a87ae1a2299230f8a06d7a87767a
Reviewed-on: https://go-review.googlesource.com/c/go/+/711137
Reviewed-by: Michael Matloob <matloob@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Matloob <matloob@google.com>

src/cmd/go/internal/modfetch/zip_sum_test/zip_sum_test.go

@@ -31,7 +31,6 @@ import (
 
 	"cmd/go/internal/cfg"
 	"cmd/go/internal/modfetch"
-	"cmd/go/internal/modload"
 
 	"golang.org/x/mod/module"
 )
@@ -94,7 +93,6 @@ func TestZipSums(t *testing.T) {
 
 	cfg.GOPROXY = "direct"
 	cfg.GOSUMDB = "off"
-	modload.Init(modload.LoaderState)
 
 	// Shard tests by downloading only every nth module when shard flags are set.
 	// This makes it easier to test small groups of modules quickly. We avoid