cmd/go/internal/modload: remove unused InitGoMod function

Change-Id: I0223d935184017e841d56abe114d78b670457c5a
Reviewed-on: https://go-review.googlesource.com/c/go/+/167437
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/internal/modload/init.go

@@ -445,13 +445,6 @@ func legacyModInit() {
 	}
 }
 
-// InitGoStmt adds a go statement, unless there already is one.
-func InitGoStmt() {
-	if modFile.Go == nil {
-		addGoStmt()
-	}
-}
-
 // addGoStmt adds a go statement referring to the current version.
 func addGoStmt() {
 	tags := build.Default.ReleaseTags