MC-17459: Coupon's expiration date and time do not match staging update end_date after creating a staging update

- Removed deprecation of coupon expiration date usage in Magento 2.2 due to backward compatibility rules

Author: dyushkin

app/code/Magento/SalesRule/Api/Data/CouponInterface.php

@@ -108,7 +108,6 @@ public function setTimesUsed($timesUsed);
      * Get expiration date
      *
      * @return string|null
-     * @deprecated Coupon expiration must follow sales rule expiration date.
      */
     public function getExpirationDate();
 
@@ -117,7 +116,6 @@ public function getExpirationDate();
      *
      * @param string $expirationDate
      * @return $this
-     * @deprecated Coupon expiration must follow sales rule expiration date.
      */
     public function setExpirationDate($expirationDate);
 

app/code/Magento/SalesRule/Model/Coupon.php

@@ -20,9 +20,6 @@ class Coupon extends \Magento\Framework\Model\AbstractExtensibleModel implements
     const KEY_USAGE_LIMIT = 'usage_limit';
     const KEY_USAGE_PER_CUSTOMER = 'usage_per_customer';
     const KEY_TIMES_USED = 'times_used';
-    /**
-     * @deprecated Coupon expiration must follow sales rule expiration date.
-     */
     const KEY_EXPIRATION_DATE = 'expiration_date';
     const KEY_IS_PRIMARY = 'is_primary';
     const KEY_CREATED_AT = 'created_at';
@@ -205,7 +202,6 @@ public function setTimesUsed($timesUsed)
      * Get expiration date
      *
      * @return string|null
-     * @deprecated Coupon expiration must follow sales rule expiration date.
      */
     public function getExpirationDate()
     {
@@ -217,7 +213,6 @@ public function getExpirationDate()
      *
      * @param string $expirationDate
      * @return $this
-     * @deprecated Coupon expiration must follow sales rule expiration date.
      */
     public function setExpirationDate($expirationDate)
     {