Revert "AOSP/Messaging - update the Messaging version to target P (28) or higher. Fixed tests in messagingtests. All tests pass/work."

This reverts commit 9752cda535.

Reason for revert: com.android.devicehealthchecks are failing https://sponge.corp.google.com/target?id=3b9a97f0-48bc-410d-94ce-0971c2f75361&target=com.android.devicehealthchecks&searchFor=&show=FAILED&sortBy=STATUS

Change-Id: I82d337b1d859083169ac6057b408f7e920f06609

tests/src/com/android/messaging/datamodel/action/GetOrCreateConversationActionTest.java

@@ -67,10 +67,8 @@ public class GetOrCreateConversationActionTest extends BugleTestCase {
         final long threadId = MmsUtils.getOrCreateThreadId(mContext, recipients);
         assertEquals(TestDataFactory.SMS_MMS_THREAD_ID_CURSOR_VALUE, threadId);
 
-        // TestDataFactory creates NUM_TEST_CONVERSATIONS conversations. blank
-        // conversation would be the next conversation.
         final String blankId = BugleDatabaseOperations.getExistingConversation(db, threadId, false);
-        assertEquals(TestDataFactory.NUM_TEST_CONVERSATIONS+1, Integer.parseInt((String)blankId));
+        assertNull("Conversation already exists", blankId);
 
         ArrayList<StubActionServiceCallLog> calls = mService.getCalls();