Remove confusing CAddrDB

The class only stores the file path, reading it from a global. Globals
are confusing and make testing harder.

The method reading from a stream does not even use any class members, so
putting it in a class is also confusing.

src/net.cpp

@@ -1749,8 +1749,7 @@ void CConnman::DumpAddresses()
 {
     int64_t nStart = GetTimeMillis();
 
-    CAddrDB adb;
-    adb.Write(addrman);
+    DumpPeerAddresses(::gArgs, addrman);
 
     LogPrint(BCLog::NET, "Flushed %d addresses to peers.dat  %dms\n",
            addrman.size(), GetTimeMillis() - nStart);