[Keyboard] Update Corne Keyboard to updated Helix split code

[drashna]

Description

Updates the Corne Keyboard to use the updated Helix type split code (mostly).

Also, this cleans up a bunch of the keymaps.
Removes both the OLED code and LAYOUT_kc from the default keymap, and creates an OLED keymap that uses the OLED_DRIVER feature, which actually supports rotating the display (so it's actually readable)

Just to make sure I have the OK's here, since I touched your code:
@foostan @epaew @JarredSteenvoorden @marksard @OMGVee @rs @the-frey

Also, I think I may update this to use Split Common instead, too.

This breaks the RGB Matrix feature completely, until the code is rewritten to support it.

Types of Changes

• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)

Issues Fixed or Closed by This PR

• Closes [Keyboard] Convert Corne Keyboard to Split Common #6001 (mutually exclusive)

Checklist

• My code follows the code style of this project.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[OMGVee]

lgtm for my keymap after cherrypicking. Thanks @drashna , you rock dude!

[the-frey]

Looks good from a glance at the code. I'll try it out ASAP.

[marksard]

LGTM, I'll try it out ASAP.

[drashna]

Well, testing with #6001 and #5998 gives a better experience, with little or no change in behavior. So I think we want to go with that change, instead.