Move private registry sources out of util package

go/extractor/toolchain/BUILD.bazel

@@ -7,7 +7,10 @@ go_library(
     srcs = ["toolchain.go"],
     importpath = "github.com/github/codeql-go/extractor/toolchain",
     visibility = ["//visibility:public"],
-    deps = ["//go/extractor/util"],
+    deps = [
+        "//go/extractor/registries",
+        "//go/extractor/util",
+    ],
 )
 
 go_test(

go/extractor/toolchain/toolchain.go

@@ -10,6 +10,7 @@ import (
 	"path/filepath"
 	"strings"
 
+	"github.com/github/codeql-go/extractor/registries"
 	"github.com/github/codeql-go/extractor/util"
 )
 
@@ -140,7 +141,7 @@ func SupportsWorkspaces() bool {
 // Constructs a `*exec.Cmd` for `go` with the specified arguments.
 func GoCommand(arg ...string) *exec.Cmd {
 	cmd := exec.Command("go", arg...)
-	util.ApplyProxyEnvVars(cmd)
+	registries.ApplyProxyEnvVars(cmd)
 	return cmd
 }