Remove duplicated hash keys for ruby 2.2

fixes some warnings on ruby 2.2:

```
ruby/2.2.0/gems/org-ruby-0.9.9/lib/org-ruby/html_symbol_replace.rb:205: warning: duplicated key at line 294 ignored: "deg"
ruby/2.2.0/gems/org-ruby-0.9.9/lib/org-ruby/html_symbol_replace.rb:234: warning: duplicated key at line 314 ignored: "sup"
ruby/2.2.0/gems/org-ruby-0.9.9/lib/org-ruby/textile_symbol_replace.rb:206: warning: duplicated key at line 295 ignored: "deg"
ruby/2.2.0/gems/org-ruby-0.9.9/lib/org-ruby/textile_symbol_replace.rb:235: warning: duplicated key at line 315 ignored: "sup"
```