Refactor Duplicated Code in KDE Connect Android-side SMS Helper

Summary:
In src/org/kde/kdeconnect/Helpers/SMSHelper.java:
getMessagesWithFilter() and getConversations() functions are now both using new function: getMessages().

Test Plan:

• Build android app and run it on android phone
• Pair it with the desktop and open sms app (kdeconnect-sms).
• Everything works as earlier, but now with refactored code.

Reviewers: sredman

Reviewed By: sredman

Subscribers: sredman, alexkovrigin, kdeconnect

Tags: KDE Connect

Maniphest Tasks: T9841

Differential Revision: https://phabricator.kde.org/D17002