remove AMD support since it conflicts with client side loaders

see issue https://github.com/linkedin/inject/pull/240

Supporting the AMD "define" syntax works only if this file is pulled down using an AMD loader.

Including this file in a script tag (for example in a concat group) after a client-side AMD loader is implemented causes a bad situation for the anonymous module -- we would have to name the module which is arguable a bad practice.

```
/* this causes issues since dust-filters-secure tries to create an anonymous module */
<script src="amdLibrary.js"></script>
<script src="dust.js"></script>
<script src="dust-filters-secure.js"></script>
```

Let's move away from the AMD support for now so that we can continue to support including this file in the browser while an AMD loader is included.


Future work will be to create a build step to output a `dust-filters-secure-amd.js` file where our file is wrapped in a define.