gh-99505: Fix docs for determining the metaclass

[robsdedude]

Alternatively, this could be less explicit but more prose by adding something along the lines of

Further, must the metaclass always be valid when removing any number of
right-most bases.

to the paragraph about the TypeError. However, I find it really hard to wrap my head around the rules if they're written in prose like that as the metaclass selection process is not necessarily super straight forward.

Closes #99505

• Issue: Resolution / determining of metaclass docs don't align with what really happens #99505

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