InstCombine/Select: remove redundant code (NFC) (#112388)

InstCombinerImpl::foldSelectInstWithICmp has some inlined code for
select-icmp-xor simplification, but this simplification is already done

InstCombine/Select: remove redundant code (NFC) (#112388)

InstCombinerImpl::foldSelectInstWithICmp has some inlined code for
select-icmp-xor simplification, but this simplification is already done
by other code, via another path:

(X & Y) == 0 ? X : X ^ Y ->
((X & Y) == 0 ? 0 : Y) ^ X ->
(X & Y) ^ X ->
X & ~Y

Cover the cases that it claims to simplify, and demonstrate that
stripping it doesn't cause test changes.

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