chore: remove redundant word in comment

[largemouth]

remove redundant word in comment

[rustbot]

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[rustbot]

compiler-builtins is developed in its own repository. If possible, consider making this change to rust-lang/compiler-builtins instead.

cc @tgross35

[tgross35]

We don't accept small typo/grammar fixes to comments as they tend to encourage spam. More substantive changes are of course welcome, however.

Thank you for the PR!