Remove Migration and fallback to destructive migration

Since UPSERT is not supported by all Android API versions and the actual data
inside the Prompts table changed along with the schema, it will be best to avoid
the effort of maintaing stale data and just rely on Room's fallback to
destructive migration, which will drop the table (and data) and create a new one
with the correct schema.

This shouldn't have many downsides as we fetch new data as soon as the app opens
and the user reaches the Dashboard. The only possible caveat is for users that
have reminders setup with Prompts enabled, that might see a notification without
Blogging Prompts if they don't open the app after updating it.

Author: Thomas Horta

fluxc/src/main/java/org/wordpress/android/fluxc/persistence/WPAndroidDatabase.kt

@@ -105,7 +105,6 @@ abstract class WPAndroidDatabase : RoomDatabase() {
                 .addMigrations(MIGRATION_18_19)
                 .addMigrations(MIGRATION_19_20)
                 .addMigrations(MIGRATION_20_21)
-                .addMigrations(MIGRATION_21_22)
                 .build()
 
         val MIGRATION_1_2 = object : Migration(1, 2) {
@@ -311,42 +310,5 @@ abstract class WPAndroidDatabase : RoomDatabase() {
                 }
             }
         }
-
-        val MIGRATION_21_22 = object : Migration(21, 22) {
-            override fun migrate(database: SupportSQLiteDatabase) {
-                // migrate old data to new table schema
-                database.apply {
-                    execSQL(
-                        "CREATE TABLE IF NOT EXISTS `BloggingPrompts_new` (" +
-                            "`id` INTEGER NOT NULL," +
-                            "`siteLocalId` INTEGER NOT NULL," +
-                            "`text` TEXT NOT NULL," +
-                            "`date` TEXT NOT NULL," +
-                            "`isAnswered` INTEGER NOT NULL," +
-                            "`respondentsCount` INTEGER NOT NULL," +
-                            "`attribution` TEXT NOT NULL," +
-                            "`respondentsAvatars` TEXT NOT NULL," +
-                            "`answeredLink` TEXT NOT NULL," +
-                            "PRIMARY KEY(`date`)" +
-                            ")"
-                    )
-
-                    val tagPrefix = "https://wordpress.com/tag/dailyprompt-"
-                    execSQL(
-                        "INSERT INTO BloggingPrompts_new (" +
-                            "id, siteLocalId, text, date, isAnswered, " +
-                            "respondentsCount, attribution, respondentsAvatars, answeredLink) " +
-                            "SELECT id, siteLocalId, text, date, isAnswered, " +
-                            "respondentsCount, attribution, respondentsAvatars, " +
-                            "'$tagPrefix' || id FROM BloggingPrompts " +
-                            "WHERE true " +
-                            "ON CONFLICT DO NOTHING"
-                    )
-
-                    execSQL("DROP TABLE `BloggingPrompts`")
-                    execSQL("ALTER TABLE `BloggingPrompts_new` RENAME TO `BloggingPrompts`")
-                }
-            }
-        }
     }
 }