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/NetdNativeService.h b/server/NetdNativeService.h
index ab2fc87..c691e91 100644
--- a/server/NetdNativeService.h
+++ b/server/NetdNativeService.h
@@ -60,7 +60,7 @@
 
     // Network and routing commands.
     binder::Status networkCreatePhysical(int32_t netId, int32_t permission) override;
-    binder::Status networkCreateVpn(int32_t netId, bool hasDns, bool secure) override;
+    binder::Status networkCreateVpn(int32_t netId, bool secure) override;
     binder::Status networkDestroy(int32_t netId) override;
 
     binder::Status networkAddInterface(int32_t netId, const std::string& iface) override;