BHV-14089: DatePicker: Incrementing year picker above 2037 results in an error

### Issue:
"this.setValue(new Date(this.localeValue.getTime()));" was not setting this.value correctly, when the year incremented past 2038. Also, setChildPickers() was modifying this.value and this.localeValue, when they had already been set in updateValue().
### Fix:
replace 
"this.setValue(new Date(this.localeValue.getTime()));"
with
"var l = this.localeValue;
this.setValue(new Date(l.year, l.month-1, l.day, l.hour, l.minute, l.second, l.millisecond));"
and delete code in setChildPickers()

Enyo-DCO-1.1-Signed-off-by: Krishna Rangarajan <krishna.rangarajan@lge.com>
Hi @kranga-lge, I believe this was placed here because `setChildPickers` can be called independently of `updateValue`, i.e. https://github.com/enyojs/moonstone/blob/master/source/DateTimePickerBase.js#L349, so I'm not sure we can remove it outright.