Confirm mnemonic with repeated words does not work

[ilanolkies]

I see this can make conflict with repeated words. If you click the second appearance of the word, the first will be removed 🤔 didn't test it out anyway

This takes me back some years when MyCrypto UI failed for me MyCryptoHQ/MyCrypto#2197

We need to remove them from the available words using the word index rather than the word as is

Originally posted by @ilanolkies in #163 (comment)