Editorial: Remove use of nonexistent [[TotalNanoseconds]] field

These are two lingering references to when time durations were a Record
with a [[TotalNanoseconds]] field.

Closes: #3021

polyfill/lib/zoneddatetime.mjs

@@ -304,7 +304,8 @@ export class ZonedDateTime {
 
       const dayLengthNs = endNs.subtract(startNs);
       const dayProgressNs = TimeDuration.fromEpochNsDiff(thisNs, startNs);
-      epochNanoseconds = dayProgressNs.round(dayLengthNs, roundingMode).add(new TimeDuration(startNs)).totalNs;
+      const roundedDayNs = dayProgressNs.round(dayLengthNs, roundingMode);
+      epochNanoseconds = roundedDayNs.addToEpochNs(startNs);
     } else {
       // smallestUnit < day
       // Round based on ISO-calendar time units

spec/plaindatetime.html

@@ -1025,7 +1025,7 @@ <h1>
         1. If CompareISODateTime(_isoDateTime1_, _isoDateTime2_) = 0, then
           1. Return 0.
         1. Let _diff_ be ? DifferenceISODateTime(_isoDateTime1_, _isoDateTime2_, _calendar_, _unit_).
-        1. If _unit_ is ~nanosecond~, return _diff_.[[Time]].[[TotalNanoseconds]].
+        1. If _unit_ is ~nanosecond~, return _diff_.[[Time]].
         1. Let _destEpochNs_ be GetUTCEpochNanoseconds(_isoDateTime2_).
         1. Return ? TotalRelativeDuration(_diff_, _destEpochNs_, _isoDateTime1_, ~unset~, _calendar_, _unit_).
       </emu-alg>

spec/zoneddatetime.html

@@ -659,7 +659,7 @@ <h1>Temporal.ZonedDateTime.prototype.round ( _roundTo_ )</h1>
           1. Let _dayLengthNs_ be ℝ(_endNs_ - _startNs_).
           1. Let _dayProgressNs_ be TimeDurationFromEpochNanosecondsDifference(_thisNs_, _startNs_).
           1. Let _roundedDayNs_ be ! RoundTimeDurationToIncrement(_dayProgressNs_, _dayLengthNs_, _roundingMode_).
-          1. Let _epochNanoseconds_ be _startNs_ + _roundedDayNs_.[[TotalNanoseconds]].
+          1. Let _epochNanoseconds_ be AddTimeDurationToEpochNanoseconds(_startNs_, _roundedDayNs_).
         1. Else,
           1. Let _roundResult_ be RoundISODateTime(_isoDateTime_, _roundingIncrement_, _smallestUnit_, _roundingMode_).
           1. Let _offsetNanoseconds_ be GetOffsetNanosecondsFor(_timeZone_, _thisNs_).