Remove "create a booking" from API docs as it's not implemented yet

[lsinger]

Describe the bug

The API docs show how to create a booking, but that's not really implemented yet -- all the props passed are still ignored.

https://woocommerce.github.io/woocommerce-bookings-api-docs/#create-a-booking-incomplete-do-not-use

To Reproduce

See the API docs above.

Expected behavior

We shouldn't advertise functionality that doesn't yet work.

Isolating the problem (mark completed items with an [x]):

• I have deactivated other plugins and confirmed this bug occurs when only the extension is active.
• I can reproduce this bug consistently using the steps above.

WordPress Environment

Details

``` Copy and paste the system status report from **WooCommerce > System Status** in WordPress admin. ```