FC-0001: remove legacy waffle flags

[dyudyunov]

This is a part of openedx/public-engineering#28

Remove all the LegacyWaffle* classes

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[natabene]

@dyudyunov Thank you for the contribution. Is this ready for our review?

[dyudyunov]

@natabene yes, this one is ready along with openedx/edx-ora2#1853 and openedx/edx-platform#30330

[robrap]

I think this is almost ready, but we can merge/release it after all uses have been removed. Feel free to squash when you are ready.

[dyudyunov]

@robrap added fixup and squashed, now it's ready to be merged! 🚀

[robrap]

Looks great. Thanks. I am going to adjust the commit comment a little when I merge.

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