Fix offenses of naming/variable_name_spec.rb
Fix offenses of naming/variable_name_spec.rb

Fix the following offenses.

```console
% bundle exec rake internal_investigation

(snip)

Offenses:

spec/rubocop/cop/naming/variable_name_spec.rb:138:5: C: Don't repeat
examples within an example group.
    it 'registers an offense for snake case in method parameter' do ...
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
spec/rubocop/cop/naming/variable_name_spec.rb:149:5: C: Don't repeat examples within an example group.
    it 'registers an offense for method arguments' do ...
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

1019 files inspected, 2 offenses detected
RuboCop failed!
```

This commit removes a redundant test. The following tests are the same.

- https://github.com/bbatsov/rubocop/blob/834262bf83f00462333245547727e102736daccd/spec/rubocop/cop/naming/variable_name_spec.rb#L138-L143
- https://github.com/bbatsov/rubocop/blob/834262bf83f00462333245547727e102736daccd/spec/rubocop/cop/naming/variable_name_spec.rb#L149-L154

I left a more clearer explanation test.

jfelchner/rubocop,akihiro17/rubocop,bbatsov/rubocop,tdeo/rubocop,sue445/rubocop,panthomakos/rubocop,mikegee/rubocop,petehamilton/rubocop,meganemura/rubocop,urbanautomaton/rubocop,scottmatthewman/rubocop,mikegee/rubocop,jmks/rubocop,urbanautomaton/rubocop,sue445/rubocop,tejasbubane/rubocop,jfelchner/rubocop,meganemura/rubocop,pocke/rubocop,jmks/rubocop,smakagon/rubocop,deivid-rodriguez/rubocop,rrosenblum/rubocop,vergenzt/rubocop,pocke/rubocop,palkan/rubocop,maxjacobson/rubocop,tejasbubane/rubocop,jmks/rubocop,bbatsov/rubocop,bquorning/rubocop,palkan/rubocop,deivid-rodriguez/rubocop,bquorning/rubocop,haziqhafizuddin/rubocop,bquorning/rubocop,panthomakos/rubocop,scottmatthewman/rubocop,jfelchner/rubocop,tdeo/rubocop,palkan/rubocop,rrosenblum/rubocop,haziqhafizuddin/rubocop,deivid-rodriguez/rubocop,maxjacobson/rubocop,panthomakos/rubocop,tdeo/rubocop,rrosenblum/rubocop,sue445/rubocop,mikegee/rubocop,petehamilton/rubocop,tejasbubane/rubocop,smakagon/rubocop,vergenzt/rubocop,akihiro17/rubocop,vergenzt/rubocop,meganemura/rubocop,akihiro17/rubocop,maxjacobson/rubocop,petehamilton/rubocop