Move private headers out of /include folder

1. The /include folder is exported by export_include_dirs attribute. The
headers for internal use should be moved to another place.
2. Remove unnecessary #inlcude from public headers. So we can have a
compact .lsdump for ABI checker.

Bug: 144407448
Test: atest
Change-Id: I5bb0df02a1ccb70f0e91f4b77668ce54e0127f62
diff --git a/res_send.cpp b/res_send.cpp
index dba7232..60c63c3 100644
--- a/res_send.cpp
+++ b/res_send.cpp
@@ -103,11 +103,11 @@
 #include "DnsTlsTransport.h"
 #include "PrivateDnsConfiguration.h"
 #include "netd_resolv/resolv.h"
-#include "netd_resolv/stats.h"
 #include "private/android_filesystem_config.h"
 #include "res_debug.h"
 #include "res_init.h"
 #include "resolv_cache.h"
+#include "stats.h"
 #include "stats.pb.h"
 #include "util.h"