Remove unused (and breaking) dependency on custom_lint (#120)

Author: filiph

samples/crossword/pubspec.yaml

@@ -24,7 +24,6 @@ dev_dependencies:
   flutter_lints: ^5.0.0
   build_runner: ^2.4.10
   built_value_generator: ^8.9.2
-  custom_lint: ^0.6.8
   riverpod_generator: ^2.6.1
   riverpod_lint: ^2.6.1