Remove/revamp kata disciplines

[FArekkusu]

As of now, kata disciplines serve no purpose. They are not shown anywhere and can't be used for kata filtering (hence, the choice is completely irrelevant), the range of available disciplines to choose from is very limited (at the same time, anything can be specified using tags), and the documentation, which is outdated and wrong, provides zero information about what this system is, or why one should use it.

Assuming disciplines indeed do nothing, I think it'd be better to get rid of them altogether (for the time being?).

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