Remove dead code from JsValue::Binary in is_truthy

[sampoder]

This is another thing flagged by @bgw's Claude:

  3. Dead duplicate match arm in is_truthy for StrictEqual (lines 2469–2494)

  ( … StrictEqual, Constant(a), Constant(b)) if a.is_value_type() => Some(a ==
  b),
  ( … StrictEqual, Constant(a), Constant(b)) if a.is_value_type() => { /* 
  same-type check */ }

  Identical pattern + guard. The second arm — the only one that handles
  cross-type equality conservatively — is unreachable. Looks like a half-applied
   fix.

I've removed the second arm with a double type check. Tests appear to still pass and I can't think of a case where we'd hit the second arm.

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[lukesandberg]

does this handle NaN correctly?

[sampoder]

No, I don't think so, see: #94172