[DOC] Remove the tutorials and users webpages

[MatthewMiddlehurst]

Part of #168.

Removes two pages from the website.

tutorials.rst links to 1.5 hour video tutorials from sktime PyData submissions. These are no longer relevant and most likely out of date. If we have similar videos in the future, this can be reintroduced in a different form. (https://www.aeon-toolkit.org/en/latest/tutorials.html)

users.rst only contains cards linking to other sections, which are already available in the sidebar. (https://www.aeon-toolkit.org/en/latest/users.html)