Register the kythe singleton on the Context instead of globally

Test: all soong tests
Change-Id: Ief43ff51e66db2d3c895b2a6952385e31b9d669b
diff --git a/cc/cc.go b/cc/cc.go
index 5e4faf2..e887fcf 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -88,7 +88,7 @@
 		ctx.TopDown("double_loadable", checkDoubleLoadableLibraries).Parallel()
 	})
 
-	android.RegisterSingletonType("kythe_extract_all", kytheExtractAllFactory)
+	ctx.RegisterSingletonType("kythe_extract_all", kytheExtractAllFactory)
 }
 
 type Deps struct {