Update purge.mdx

Author: JakeChampion

documentation/docs/fastly:cache/SimpleCache/purge.mdx

@@ -26,14 +26,6 @@ purge(key, options)
     - Possible values are:
       - "global" - This will remove the content from all of Fastly.
       - "pop" - This will remove the content from the POP that contains the currently executing instance.
-  - `headers`
-    - : Any headers you want to add to your request, contained
-      within a `Headers` object or an object literal with `String` values.
-  - `body`
-    - : Any body that you want to add to your request: this can be an `ArrayBuffer`, a `TypedArray`, a `DataView`, a `URLSearchParams`, string object or literal, or a `ReadableStream` object.
-  - `backend` _**Fastly-specific**_
-  - `cacheOverride` _**Fastly-specific**_
-  - `cacheKey` _**Fastly-specific**_
 
 ### Return value