switch annotation to internal in BaseKey

Author: kolea2

google-cloud-datastore/src/main/java/com/google/cloud/datastore/BaseKey.java

@@ -20,7 +20,7 @@
 import static com.google.cloud.datastore.Validator.validateNamespace;
 import static com.google.cloud.datastore.Validator.validateProjectId;
 
-import com.google.api.core.BetaApi;
+import com.google.api.core.InternalApi;
 import com.google.common.base.MoreObjects;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
@@ -117,7 +117,7 @@ public B setNamespace(String namespace) {
     }
 
     /** Sets the database id of the key. */
-    @BetaApi
+    @InternalApi
     public B setDatabaseId(String databaseId) {
       this.databaseId = databaseId;
       return self();