Stop setting net.dns{1234} system properties.

Nothing in the system consumes these properties, they were never part
of an official public API, and they can leak information about the
current network to applications without networking prvileges.

Specifically, these properites allow applications to access network state
(and detect network changes, etc.) without having the ACCESS_NETWORK_STATE
permission.

Test: runtest ConnectivityServiceTest passes
Bug: 33308258
Change-Id: I85abc52bc11aee33940fd0af2397478a9a5c3b8f

services/core/java/com/android/server/ConnectivityService.java

@@ -4615,28 +4615,9 @@ public class ConnectivityService extends IConnectivityManager.Stub
         } catch (Exception e) {
             loge("Exception in setDnsConfigurationForNetwork: " + e);
         }
-        final NetworkAgentInfo defaultNai = getDefaultNetwork();
-        if (defaultNai != null && defaultNai.network.netId == netId) {
-            setDefaultDnsSystemProperties(dnses);
-        }
         flushVmDnsCache();
     }
 
-    private void setDefaultDnsSystemProperties(Collection<InetAddress> dnses) {
-        int last = 0;
-        for (InetAddress dns : dnses) {
-            ++last;
-            String key = "net.dns" + last;
-            String value = dns.getHostAddress();
-            SystemProperties.set(key, value);
-        }
-        for (int i = last + 1; i <= mNumDnsEntries; ++i) {
-            String key = "net.dns" + i;
-            SystemProperties.set(key, "");
-        }
-        mNumDnsEntries = last;
-    }
-
     private String getNetworkPermission(NetworkCapabilities nc) {
         // TODO: make these permission strings AIDL constants instead.
         if (!nc.hasCapability(NET_CAPABILITY_NOT_RESTRICTED)) {
@@ -4853,7 +4834,6 @@ public class ConnectivityService extends IConnectivityManager.Stub
         notifyLockdownVpn(newNetwork);
         handleApplyDefaultProxy(newNetwork.linkProperties.getHttpProxy());
         updateTcpBufferSizes(newNetwork);
-        setDefaultDnsSystemProperties(newNetwork.linkProperties.getDnsServers());
     }
 
     private void processListenRequests(NetworkAgentInfo nai, boolean capabilitiesChanged) {