alts: Use normal defaults in Alts{Channel,Server}Builder

The ALTS builders are supposed to act like ChannelCreds, as done in
other languages. ChannelCreds don't have the opportunity to change
settings like this. In addition, the options here weren't set in
GoogleDefaultChannelBuilder and ComputeEngineChannelBuilder.
diff --git a/alts/src/main/java/io/grpc/alts/AltsChannelBuilder.java b/alts/src/main/java/io/grpc/alts/AltsChannelBuilder.java
index 8252884..8e61e2a 100644
--- a/alts/src/main/java/io/grpc/alts/AltsChannelBuilder.java
+++ b/alts/src/main/java/io/grpc/alts/AltsChannelBuilder.java
@@ -41,7 +41,6 @@
 import io.grpc.internal.SharedResourcePool;
 import io.grpc.netty.InternalNettyChannelBuilder;
 import io.grpc.netty.NettyChannelBuilder;
-import java.util.concurrent.TimeUnit;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 import javax.annotation.Nullable;
@@ -74,11 +73,7 @@
   }
 
   private AltsChannelBuilder(String target) {
-    delegate =
-        NettyChannelBuilder.forTarget(target)
-            .keepAliveTime(20, TimeUnit.SECONDS)
-            .keepAliveTimeout(10, TimeUnit.SECONDS)
-            .keepAliveWithoutCalls(true);
+    delegate = NettyChannelBuilder.forTarget(target);
     InternalNettyChannelBuilder.setProtocolNegotiatorFactory(
         delegate(), new ProtocolNegotiatorFactory());
   }
diff --git a/alts/src/main/java/io/grpc/alts/AltsServerBuilder.java b/alts/src/main/java/io/grpc/alts/AltsServerBuilder.java
index 7cffef0..8c8d557 100644
--- a/alts/src/main/java/io/grpc/alts/AltsServerBuilder.java
+++ b/alts/src/main/java/io/grpc/alts/AltsServerBuilder.java
@@ -70,13 +70,7 @@
 
   /** Creates a gRPC server builder for the given port. */
   public static AltsServerBuilder forPort(int port) {
-    NettyServerBuilder nettyDelegate =
-        NettyServerBuilder.forAddress(new InetSocketAddress(port))
-            .maxConnectionIdle(1, TimeUnit.HOURS)
-            .keepAliveTime(270, TimeUnit.SECONDS)
-            .keepAliveTimeout(20, TimeUnit.SECONDS)
-            .permitKeepAliveTime(10, TimeUnit.SECONDS)
-            .permitKeepAliveWithoutCalls(true);
+    NettyServerBuilder nettyDelegate = NettyServerBuilder.forAddress(new InetSocketAddress(port));
     return new AltsServerBuilder(nettyDelegate);
   }