I just removed the call site nil, and it broke some tests. The failure looks like this:

```
Failure/Error: reset object
       expected "Unable to remove stub method foo because the object was frozen. Warning generated from spec at `./spec/rspec/mocks/matchers/receive_spec.rb:217`. Called from /Users/sam/dev/rspec/rspec-dev/repos/rspec-mocks/spec/spec_helper.rb:29:in `reset'." not to match /Called from/
       Diff:
       @@ -1,2 +1,2 @@
       -/Called from/
       +"Unable to remove stub method foo because the object was frozen. Warning generated from spec at `./spec/rspec/mocks/matchers/receive_spec.rb:217`. Called from /Users/sam/dev/rspec/rspec-dev/repos/rspec-mocks/spec/spec_helper.rb:29:in `reset'."
```