Convert KMail serial number to use Akonadi Item ID instead

KMail identifies its emails by Akonadi Item ID now.

src/alarmtext.cpp

@@ -303,11 +303,6 @@ bool AlarmText::isTodo() const
     return d->mType == Private::Todo;
 }
 
-unsigned long AlarmText::kmailSerialNumber() const
-{
-    return static_cast<unsigned long>(akonadiItemId());
-}
-
 Akonadi::Item::Id AlarmText::akonadiItemId() const
 {
     return d->mAkonadiItemId;

src/alarmtext.h

@@ -158,14 +158,8 @@ public:
     /** Return whether the instance contains the text of a todo. */
     bool isTodo() const;
 
-    /** Return the kmail serial number of an email.
-     *  @return serial number, or 0 if none.
-     *  @deprecated Use akonadiItemId() instead
-     */
-    KALARMCAL_DEPRECATED unsigned long kmailSerialNumber() const;
-
     /** Return the Akonadi item ID of an email.
-     *  @return serial number, or 0 if none.
+     *  @return Item ID, or -1 if none.
      */
     Akonadi::Item::Id akonadiItemId() const;