Remove migration note for StreamableHTTPASGIApp

The class was never intended to be a public API, so no migration
documentation is needed.

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Author: maxisbey

docs/migration.md

@@ -222,22 +222,6 @@ Affected types:
 
 The `ClientSession.read_resource()`, `subscribe_resource()`, and `unsubscribe_resource()` methods now accept both `str` and `AnyUrl` for backwards compatibility.
 
-### `StreamableHTTPASGIApp` moved to `streamable_http_manager` module
-
-The `StreamableHTTPASGIApp` class has been moved from `mcp.server.fastmcp.server` to `mcp.server.streamable_http_manager`.
-
-**Before (v1):**
-
-```python
-from mcp.server.fastmcp.server import StreamableHTTPASGIApp
-```
-
-**After (v2):**
-
-```python
-from mcp.server.streamable_http_manager import StreamableHTTPASGIApp
-```
-
 ## Deprecations
 
 <!-- Add deprecations below -->