Avoid duplicate module names in the error from ModuleForTests.

#codehealth

Test: m nothing
Change-Id: Ia7c3191440452ce04782701bc6ef99251e55af4d
diff --git a/android/testing.go b/android/testing.go
index e25e5c5..bd2faa2 100644
--- a/android/testing.go
+++ b/android/testing.go
@@ -509,12 +509,11 @@
 				allVariants = append(allVariants, ctx.ModuleSubDir(m))
 			}
 		})
-		sort.Strings(allModuleNames)
 		sort.Strings(allVariants)
 
 		if len(allVariants) == 0 {
 			panic(fmt.Errorf("failed to find module %q. All modules:\n  %s",
-				name, strings.Join(allModuleNames, "\n  ")))
+				name, strings.Join(SortedUniqueStrings(allModuleNames), "\n  ")))
 		} else {
 			panic(fmt.Errorf("failed to find module %q variant %q. All variants:\n  %s",
 				name, variant, strings.Join(allVariants, "\n  ")))