cmd/go/internal/modload: revert duplicate path suppression in modload.ImportMissingError

CL 210338 suppressed duplication for import paths mentioned in an
ImportMissingError.

Unfortunately, that broke one of the cases in
cmd/go/internal/modload.TestImport, and the new error message is still
kind of awkward anyway.

Let's revert that part of the change — we can try again with more
coverage for that case.

Updates #35986

Change-Id: Ib0858aec4f89a7231e32c35ec876da80d80f2098
Reviewed-on: https://go-review.googlesource.com/c/go/+/210342
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

src/cmd/go/internal/modload/import.go

@@ -42,9 +42,6 @@ func (e *ImportMissingError) Error() string {
 		if search.IsStandardImportPath(e.Path) {
 			return fmt.Sprintf("package %s is not in GOROOT (%s)", e.Path, filepath.Join(cfg.GOROOT, "src", e.Path))
 		}
-		if i := load.ImportPathError(nil); errors.As(e.QueryErr, &i) {
-			return fmt.Sprintf("cannot find module: %v", e.QueryErr)
-		}
 		if e.QueryErr != nil {
 			return fmt.Sprintf("cannot find module providing package %s: %v", e.Path, e.QueryErr)
 		}