Remove unnecessary Dark Mode CSS

[mquevill]

These CSS changes are no longer necessary. Most of them are not even selectors on the page any more. I tested these one at a time and couldn't see any changes visually and checked for the selectors too.

Fixes #2180.
Fixes #2194.

[mquevill]

In the newest round of Facebook's redesign, this actually needs to be removed, otherwise the bottom of the page is partially off the screen (See the button on the bottom left being cut off below)

[WrayOfSunshine]

I literally just reported the cut off thing as an issue for dark mode, nice to see the code update to fix it is already ready already!

[agret]

While you are updating darkmode CSS, when you have a chat that uses a Messenger theme the text box will be light too which makes your writing impossible to read. Can you make the input box always dark? This issue makes it very hard to message some people.

[devCKVargas]

While you are updating darkmode CSS, when you have a chat that uses a Messenger theme the text box will be light too which makes your writing impossible to read. Can you make the input box always dark? This issue makes it very hard to message some people.

Checkout #2196 for a temporary fix

[dxwil]

Any updates on this? Happens to me...