Remove sdkPreSingleton and overlaySingleton

These were the only 2 pre-singletons in soong. sdkPreSingleton is
totally unused. overlaySingleton can be done during
GenerateAndroidBuildActions instead.

Test: m nothing --no-skip-soong-tests
Change-Id: Ieb5ab92f18cb56be4049c0842f61df8aa02dc52c
diff --git a/java/android_manifest_test.go b/java/android_manifest_test.go
index 0a39dca..5909b1e 100644
--- a/java/android_manifest_test.go
+++ b/java/android_manifest_test.go
@@ -78,10 +78,7 @@
 		}
 	`
 
-	result := android.GroupFixturePreparers(
-		PrepareForTestWithJavaDefaultModules,
-		PrepareForTestWithOverlayBuildComponents,
-	).RunTestWithBp(t, bp)
+	result := PrepareForTestWithJavaDefaultModules.RunTestWithBp(t, bp)
 
 	manifestMergerRule := result.ModuleForTests("app", "android_common").Rule("manifestMerger")
 	android.AssertPathRelativeToTopEquals(t, "main manifest",
@@ -129,10 +126,7 @@
 
 	`
 
-	result := android.GroupFixturePreparers(
-		PrepareForTestWithJavaDefaultModules,
-		PrepareForTestWithOverlayBuildComponents,
-	).RunTestWithBp(t, bp)
+	result := PrepareForTestWithJavaDefaultModules.RunTestWithBp(t, bp)
 
 	manifestMergerRule := result.ModuleForTests("test", "android_common").Rule("manifestMerger")
 	android.AssertStringMatches(t,