docs(http): remove unimplemented deserializeStream handler property

The content-type handler interface table documented a
`deserializeStream(stream)` property that Harper does not implement. The
`ContentTypeHandler` interface in the core repo declares only `serialize`,
`serializeStream`, `deserialize`, and `q`.

Removes the `deserializeStream` row and drops the now-dangling "Used when
`deserializeStream` is absent." clause from the `deserialize(buffer)`
description.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: Ethan-Arrowood

reference/http/api.md

@@ -434,13 +434,12 @@ contentTypes.set('text/xml', {
 
 ### Handler Interface
 
-| Property                    | Type                                      | Description                                                                                                                        |
-| --------------------------- | ----------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------- |
-| `serialize(data)`           | `(any) => Buffer \| Uint8Array \| string` | Serialize data for a response                                                                                                      |
-| `serializeStream(data)`     | `(any) => ReadableStream`                 | Serialize as a stream (for async iterables or large data)                                                                          |
-| `deserialize(buffer)`       | `(Buffer \| string) => any`               | Deserialize an incoming request body. Used when `deserializeStream` is absent. String for `text/*` types, Buffer for binary types. |
-| `deserializeStream(stream)` | `(ReadableStream) => any`                 | Deserialize an incoming request stream                                                                                             |
-| `q`                         | number (0–1)                              | Quality indicator for content negotiation. Defaults to `1`.                                                                        |
+| Property                | Type                                      | Description                                                                               |
+| ----------------------- | ----------------------------------------- | ----------------------------------------------------------------------------------------- |
+| `serialize(data)`       | `(any) => Buffer \| Uint8Array \| string` | Serialize data for a response                                                             |
+| `serializeStream(data)` | `(any) => ReadableStream`                 | Serialize as a stream (for async iterables or large data)                                 |
+| `deserialize(buffer)`   | `(Buffer \| string) => any`               | Deserialize an incoming request body. String for `text/*` types, Buffer for binary types. |
+| `q`                     | number (0–1)                              | Quality indicator for content negotiation. Defaults to `1`.                               |
 
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