Remove context copying from run_async function

This was required with the previous implementation of Werkzeug's
locals which didn't persist across threads. However as the current
implementation uses ContextVars which do persist the context copying
is no longer required.

src/flask/helpers.py

@@ -819,33 +819,8 @@ def run_async(func: t.Callable[..., t.Coroutine]) -> t.Callable[..., t.Any]:
         )
 
     @wraps(func)
-    def outer(*args: t.Any, **kwargs: t.Any) -> t.Any:
-        """This function grabs the current context for the inner function.
-
-        This is similar to the copy_current_xxx_context functions in the
-        ctx module, except it has an async inner.
-        """
-        ctx = None
-
-        if _request_ctx_stack.top is not None:
-            ctx = _request_ctx_stack.top.copy()
-
-        @wraps(func)
-        async def inner(*a: t.Any, **k: t.Any) -> t.Any:
-            """This restores the context before awaiting the func.
-
-            This is required as the function must be awaited within the
-            context. Only calling ``func`` (as per the
-            ``copy_current_xxx_context`` functions) doesn't work as the
-            with block will close before the coroutine is awaited.
-            """
-            if ctx is not None:
-                with ctx:
-                    return await func(*a, **k)
-            else:
-                return await func(*a, **k)
-
-        return async_to_sync(inner)(*args, **kwargs)
+    def wrapper(*args: t.Any, **kwargs: t.Any) -> t.Any:
+        return async_to_sync(func)(*args, **kwargs)
 
-    outer._flask_sync_wrapper = True  # type: ignore
-    return outer
+    wrapper._flask_sync_wrapper = True  # type: ignore
+    return wrapper