Remove brackets from method/function signatures in docs

[Tim Graham]

According to the ​spinx docs, "For functions with optional parameters that don’t have default values (typically functions implemented in C extension modules without keyword argument support), you can use brackets to specify the optional parts". Not sure how our docs got in the habit of using brackets, but it doesn't seem like we should be doing that.

Brackets should be removed from things like:

.. function:: create_test_db([verbosity=1, autoclobber=False, serialize=True, keepdb=False])

and missing kwarg defaults should be added in places like:

.. function:: password_reset_confirm(request[, uidb64, token, template_name, token_generator, set_password_form, post_reset_redirect, current_app, extra_context])

Find the places to update with grep -rI "\[" * | grep 'function::' and grep -rI "\[" * | grep 'method::'.

[Tim Graham]

​PR

[Tim Graham <timograham@…>]

In 87d5508:

Fixed #25159 -- Removed brackets from class/function/method signatures in docs.

Thanks hellbeast for the initial patch.

[Tim Graham <timograham@…>]

In a66d843:

[1.8.x] Fixed #25159 -- Removed brackets from class/function/method signatures in docs.

Thanks hellbeast for the initial patch.

Backport of 87d55081ea398c65b2503d22ed3907a9175ec729 from master