Remove getHasDns() and VirtualNetwork.mHasDns

getHasDns() and VirtualNetwork.mHasDns are no more useful after commit
aops/658122.

Bug: 116539103
Test: system/netd/tests/runtests.sh pass

Change-Id: Ica04984a954a9e89a5eb38a9b262775d686f8ed4
diff --git a/server/VirtualNetwork.cpp b/server/VirtualNetwork.cpp
index 974f918..33791c6 100644
--- a/server/VirtualNetwork.cpp
+++ b/server/VirtualNetwork.cpp
@@ -28,16 +28,9 @@
 namespace android {
 namespace net {
 
-VirtualNetwork::VirtualNetwork(unsigned netId, bool hasDns, bool secure) :
-        Network(netId), mHasDns(hasDns), mSecure(secure) {
-}
+VirtualNetwork::VirtualNetwork(unsigned netId, bool secure) : Network(netId), mSecure(secure) {}
 
-VirtualNetwork::~VirtualNetwork() {
-}
-
-bool VirtualNetwork::getHasDns() const {
-    return mHasDns;
-}
+VirtualNetwork::~VirtualNetwork() {}
 
 bool VirtualNetwork::isSecure() const {
     return mSecure;