Removed redundant max_connections variable definition.

In templates/my.cnf.erb the max_connections variable is defined twice:

```
...
max_connections = <%= @max_connections %>
...
<% if @max_connections != 'UNSET' -%>
max_connections     = <%= @max_connections %>
<% end -%>
...
```

This pull request removes the first definition.

Tests are green:

```
$ bundle exec rake spec
...
Finished in 8.66 seconds
162 examples, 0 failures
```