Fix analyzer hints and warnings in test/.

test/transformer/configuration/with_configuration_only_instantiates_configurable_transformers_test.dart

Index: test/transformer/configuration/with_configuration_only_instantiates_configurable_transformers_test.dart
diff --git a/test/transformer/configuration/with_configuration_only_instantiates_configurable_transformers_test.dart b/test/transformer/configuration/with_configuration_only_instantiates_configurable_transformers_test.dart
index 6b480c5bc74fd5a901504c22d303f41d4bdc6a78..2ed42802209ddbb7213e772f212fdf7a69111fd3 100644
--- a/test/transformer/configuration/with_configuration_only_instantiates_configurable_transformers_test.dart
+++ b/test/transformer/configuration/with_configuration_only_instantiates_configurable_transformers_test.dart
@@ -68,7 +68,7 @@ main() {
      ]).create();
 
      pubGet();
-     var server = pubServe();
+     pubServe();
      requestShouldSucceed("foo.json", JSON.encode(configuration));
      requestShould404("foo.out");
      endPubServe();