Make time dependency optional (#7425)

Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

esphome/components/datetime/datetime_entity.cpp

@@ -192,6 +192,7 @@ void DateTimeEntityRestoreState::apply(DateTimeEntity *time) {
   time->publish_state();
 }
 
+#ifdef USE_TIME
 static const int MAX_TIMESTAMP_DRIFT = 900;  // how far can the clock drift before we consider
                                              // there has been a drastic time synchronization
 
@@ -245,6 +246,7 @@ bool OnDateTimeTrigger::matches_(const ESPTime &time) const {
          time.day_of_month == this->parent_->day && time.hour == this->parent_->hour &&
          time.minute == this->parent_->minute && time.second == this->parent_->second;
 }
+#endif
 
 }  // namespace datetime
 }  // namespace esphome