docs: remove "to-do" section

Moved all the to-do items to the following github issues:

* #10479
* #10480
* #10481

Signed-off-by: Jeff Squyres <[email protected]>

Author: jsquyres

docs/index.rst

@@ -64,7 +64,6 @@ Table of contents
    :maxdepth: 2
    :numbered:
 
-   to-do
    quickstart
    getting-help
    release-notes/index