Replace com.google.common.base.Function with java.util.function.Function

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=179249159

java/google/registry/request/Modules.java

@@ -33,7 +33,6 @@ import com.google.appengine.api.urlfetch.URLFetchService;
 import com.google.appengine.api.urlfetch.URLFetchServiceFactory;
 import com.google.appengine.api.users.UserService;
 import com.google.appengine.api.users.UserServiceFactory;
-import com.google.common.base.Function;
 import com.google.common.collect.ImmutableSet;
 import dagger.Binds;
 import dagger.Module;
@@ -43,6 +42,7 @@ import google.registry.keyring.api.KeyModule.Key;
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.util.Set;
+import java.util.function.Function;
 import javax.inject.Named;
 import javax.inject.Provider;
 import javax.inject.Singleton;

java/google/registry/request/Route.java

@@ -15,7 +15,7 @@
 package google.registry.request;
 
 import com.google.auto.value.AutoValue;
-import com.google.common.base.Function;
+import java.util.function.Function;
 
 /**
  * Mapping of an {@link Action} to a {@link Runnable} instantiator for request handling.

java/google/registry/request/Router.java

@@ -17,7 +17,6 @@ package google.registry.request;
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Throwables.throwIfUnchecked;
 
-import com.google.common.base.Function;
 import com.google.common.collect.ImmutableSortedMap;
 import com.google.common.collect.Ordering;
 import java.lang.reflect.InvocationTargetException;
@@ -25,6 +24,7 @@ import java.lang.reflect.Method;
 import java.util.Map;
 import java.util.Optional;
 import java.util.TreeMap;
+import java.util.function.Function;
 
 /**
  * Path prefix request router.