This has the side effect of modifying the passed in hash.  Consider a case like this:

``` ruby
RSpec.configure do |c|
  focused_options = { focus: true, toplevel_alias: true }
  c.alias_example_group_to :focus, focused_options
  c.alias_example_group_to :focused, focused_options
end
```

The 2nd one will not work properly because the first one modifies the passed in options.

I think it's better to dup the hash before deleting from it.