Sync against taskchampion-sync-server (#3118)

This removes use of gnutls and the TLS implementation, which is no
longer needed (task synchronization is handled via Taskchampion, which
uses `reqwest`, which handles TLS via other Rust dependencies). This
incidentally removes the following config options:
 * `debug.tls`
 * `taskd.ca`
 * `taskd.certificate`
 * `taskd.ciphers`
 * `taskd.credentials`
 * `taskd.key`
 * `taskd.server`
 * `taskd.trust`

src/TDB2.cpp

@@ -41,6 +41,7 @@
 #include <format.h>
 #include <main.h>
 #include <util.h>
+#include "tc/Server.h"
 
 bool TDB2::debug_mode = false;
 static void dependency_scan (std::vector<Task> &);
@@ -469,6 +470,12 @@ int TDB2::num_reverts_possible ()
   return (int)replica.num_undo_points ();
 }
 
+////////////////////////////////////////////////////////////////////////////////
+void TDB2::sync (tc::Server server, bool avoid_snapshots)
+{
+  replica.sync(std::move(server), avoid_snapshots);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 void TDB2::dump ()
 {