cleanup: remove unused dep_dependency on cli_util (#336)

Author: kevmoo

pubspec.yaml

@@ -1,5 +1,5 @@
 name: source_gen
-version: 0.8.1+3
+version: 0.8.2-dev
 author: Dart Team <[email protected]>
 description: Automated source code generation for Dart.
 homepage: https://github.com/dart-lang/source_gen
@@ -15,7 +15,6 @@ dependencies:
 dev_dependencies:
   build_test: ">0.9.0 <0.11.0"
   collection: ^1.1.2
-  cli_util: '>=0.1.0 <0.2.0'
   test: ^0.12.3
   _test_annotations:
     path: ./_test_annotations