Editorial: Assert CreateTimeDurationRecord is called with valid durat…

…ion values

All callers to CreateTimeDurationRecord pass valid duration values, so
we can assert this in CreateTimeDurationRecord instead of throwing an
error.

spec/duration.html

@@ -889,7 +889,7 @@ <h1>
         <dd>It returns a Time Duration Record.</dd>
       </dl>
       <emu-alg>
-        1. If ! IsValidDuration(0, 0, 0, _days_, _hours_, _minutes_, _seconds_, _milliseconds_, _microseconds_, _nanoseconds_) is *false*, throw a *RangeError* exception.
+        1. Assert: ! IsValidDuration(0, 0, 0, _days_, _hours_, _minutes_, _seconds_, _milliseconds_, _microseconds_, _nanoseconds_) is *true*.
         1. Return the Record {
             [[Days]]: ℝ(𝔽(_days_)),
             [[Hours]]: ℝ(𝔽(_hours_)),