openapi: Fix minor assertion in curl examples.

Now, include and exclude configuration
are fetched from openapi data, and only
one type can be encoded for every example.

This removes the need for the assertion to
test if both include and exclude are present
since at a time, only one can be present.

zerver/openapi/markdown_extension.py

@@ -259,8 +259,6 @@ def generate_curl_example(
     exclude: Optional[List[str]] = None,
     include: Optional[List[str]] = None,
 ) -> List[str]:
-    if exclude is not None and include is not None:
-        raise AssertionError("exclude and include cannot be set at the same time.")
 
     lines = ["```curl"]
     operation = endpoint + ":" + method.lower()