Java: Minor fixup for SSA AdjacentUsesImpl::varBlockReaches
Java: Minor fixup for SSA AdjacentUsesImpl::varBlockReaches

This should not change anything in regards to correctness overall -- what we
really care about is `varBlockStep`, and that checks `varOccursInBlock(v, b2)`.
However, the comment is a bit easier to read together with the code
now (and probably also gives slightly smaller predicate result size).

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