Remove 'Contents' section from the Configuration Manual

[anoadragon453]

https://matrix-org.github.io/synapse/latest/usage/configuration/config_documentation.html#contents

Seems redundant when we have a Table of Contents sidebar?

Potentially related: #12752. cc @H-Shay.

[H-Shay]

What browser are you using? I don't see a table of contents sidebar on Firefox, the greater docs sidebar shows up but that's it...

[aaronraimist]

It shows up for me in Firefox. You may not see it because there is a minimum window width before it is shown.

[anoadragon453]

I sometimes notice the ToC not showing up on certain computers as well, and we might want to consider lowering the minimum width.

@H-Shay could I ask what your screen resolution in pixels in? 😁

[H-Shay]

Ah yes when I expanded the window to the entire screen I could see it. My screen resolution is 1920x1080.