Revert "Add version validation for LookupMap, also add unittest directly in LookupMap."

pkg/lookup_map/lib/lookup_map.dart

Index: pkg/lookup_map/lib/lookup_map.dart
diff --git a/pkg/lookup_map/lib/lookup_map.dart b/pkg/lookup_map/lib/lookup_map.dart
index 0c03094e680e8590419a0c537798c054e9aef8c5..609f854288d10088c23cfc397cbda82b4ea84aeb 100644
--- a/pkg/lookup_map/lib/lookup_map.dart
+++ b/pkg/lookup_map/lib/lookup_map.dart
@@ -91,10 +91,3 @@ class LookupMap<K, V> {
 /// An expando that stores a flatten version of a [LookupMap], this is
 /// computed and stored the first time the map is accessed.
 final _flatMap = new Expando('_flat_map');
-
-/// Internal constant that matches the version in the pubspec. This is used by
-/// dart2js to ensure that optimizations are only enabled on known versions of
-/// this code.
-// Note: this needs to be kept in sync with the pubspec, otherwise
-// test/version_check_test would fail.
-final _version = '0.0.1';