Merge libnetddns into libnetd_resolv

libnetddns is the library for DNS-over-TLS and is statically
linked to netd. Deprecate it and move them to libnetd_resolv
as a more general DNS library for netd.

This change comprises:

[1] Clean up netd/server/dns/*. Move all DnsTls* files to
    netd/resolv/ to parts of libnetd_resolv library.

[2] Export DnsTls* classes being visible for netd. It will only
    be temporary for a while.

[3] Remove the libssl dependency in netd. The relevant stuff is
    moved to libnetd_resolv.

Note that DnsTls* classes are still required for DnsProxyListener
and ResolverController to manipulate private DNS servers even after
this change.

Bug: 113628807
Test: as follows
    - built, flashed, booted
    - system/netd/tests/runtests.sh
    - DNS-over-TLS in live network passed

Change-Id: Ieac5889b4ebe737f876b3dcbe1a8da2b2b1b629d
diff --git a/server/NetdNativeService.cpp b/server/NetdNativeService.cpp
index d1c0377..d589bfc 100644
--- a/server/NetdNativeService.cpp
+++ b/server/NetdNativeService.cpp
@@ -38,7 +38,7 @@
 #include "DumpWriter.h"
 #include "EventReporter.h"
 #include "InterfaceController.h"
-#include "NetdConstants.h"
+#include "NetdConstants.h"  // SHA256_SIZE
 #include "NetdNativeService.h"
 #include "Permission.h"
 #include "Process.h"