Normative: fix invalid assertion in Number::lessThan

spec.html

@@ -2127,7 +2127,7 @@ <h1>
             1. If _y_ is *+∞*<sub>𝔽</sub>, return *true*.
             1. If _y_ is *-∞*<sub>𝔽</sub>, return *false*.
             1. If _x_ is *-∞*<sub>𝔽</sub>, return *true*.
-            1. Assert: _x_ and _y_ are finite and non-zero.
+            1. Assert: _x_ and _y_ are finite.
             1. If ℝ(_x_) &lt; ℝ(_y_), return *true*. Otherwise, return *false*.
           </emu-alg>
         </emu-clause>