Remove unused Cheetah.Servlet.Servlet.request

This is unused except in `Cheetah.Template.Template.webInput` method.  Which somewhat clearly states (in some odd english) in its documentation: 
```
This only in a subclass that also inherits from Webware's Servlet or
HTTPServlet. Otherwise you'll get an AttributeError on 'self.request'.
```

I ran the tests and none of them were failing that weren't failing `master`

The motivation for this change is as follows:

We're attempting to add `$request` to the `searchList` as this is needed for ~90% of #webcore refactors.  However, the template instance itself is always first in the `searchList` (err well actually second, behind an empty dictionary.  Could potentially save a list operation and a dictionary operation for every searchlist lookup by removing this, but that's for another day) and since the template instance is always first it finds the class attribute `Cheetah.Servlet.Servlet.request` before it finds our `{'request': request}` in the `searchList`.  For now, we're probably going to do the following "hack / workaround":

```python
def instantiate_cheetah_template(...):
    # Greatly simplified
    # Support our modified get_var_from_search_list which ignores the template instance
    search_list = [{'request': request}]

    instance = cheetah_template_cls(...)
    # Make this show up before the class attribute
    instance.request = request

    return instance
```