tree-sitter gives an arrow with one unparenthesised parameter a `parameter`
field (singular) and no `parameters` list node, so `_js_local_bound_names`
never saw it: `x => sink(x)` bound nothing, and `x` read as a by-name
reference to any same-named callable in the corpus, fabricating an
indirect_call edge (INFERRED, 0.8).
The parenthesised form was always handled, so `(x) => …` and `x => …`
behaved differently. Same singular/plural trap as `catch_clause.parameter`.
Strictly subtractive on real code: +0/-88 indirect_call edges over 5,402
files of node_modules, +0/-98 over a 6,000-file mixed corpus.
