Remove another deprecated import from the API documentation.

jsonschema.FormatError is already deprecated at this import path,
instead in favor of jsonschema.exceptions.FormatError.

Author: Julian

docs/api/index.rst

@@ -17,7 +17,7 @@ Submodules
 .. automodule:: jsonschema
    :members:
    :imported-members:
-   :exclude-members: Validator
+   :exclude-members: FormatError, Validator
 
 .. autodata:: jsonschema._format._F