fix(ui5-timepicker): fix firing "change" event for the same value

[ilhan007]

Previously the TImePicker used to fire "change" event unconditionally upon "Submit" press.
Now, the value is checked and if it is changed, the event will be fired.

Additionally, the following has been removed from the constructor as these are existing boolean properties that by default are false

this.readonly = false;
this.disabled = false;