arm64: itx: Remove a todo comment about more special cased functions
arm64: itx: Remove a todo comment about more special cased functions

These cases were removed from x86 to save space and simplify the code
in e0b88bd2b2c97a2695edcc498485e1cb3003e7f1, as those cases
were essentially unused in real world bitstreams.

xiph/rav1e,xiph/rav1e