Remove Backend.isDeleteMoveToTrash()

This property is confusing and basically unused right now.

app/core/src/main/java/com/fsck/k9/controller/MessagingController.java

@@ -2028,8 +2028,7 @@ public class MessagingController {
             boolean isSpamFolder = account.hasSpamFolder() && account.getSpamFolderId() == folderId;
             boolean doNotMoveToTrashFolder = skipTrashFolder ||
                 !account.hasTrashFolder() || folderId == trashFolderId ||
-                isSpamFolder ||
-                (backend.getSupportsTrashFolder() && !backend.isDeleteMoveToTrash());
+                isSpamFolder;
 
             LocalFolder localTrashFolder = null;
             if (doNotMoveToTrashFolder) {

backend/api/src/main/java/com/fsck/k9/backend/api/Backend.kt

@@ -15,7 +15,6 @@ interface Backend {
     val supportsTrashFolder: Boolean
     val supportsSearchByDate: Boolean
     val isPushCapable: Boolean
-    val isDeleteMoveToTrash: Boolean
 
     @Throws(MessagingException::class)
     fun refreshFolderList()

backend/demo/src/main/java/app/k9mail/backend/demo/DemoBackend.kt

@@ -36,7 +36,6 @@ class DemoBackend(private val backendStorage: BackendStorage) : Backend {
     override val supportsTrashFolder: Boolean = true
     override val supportsSearchByDate: Boolean = false
     override val isPushCapable: Boolean = false
-    override val isDeleteMoveToTrash: Boolean = true
 
     override fun refreshFolderList() {
         val localFolderServerIds = backendStorage.getFolderServerIds().toSet()

backend/imap/src/main/java/com/fsck/k9/backend/imap/ImapBackend.kt

@@ -45,7 +45,6 @@ class ImapBackend(
     override val supportsTrashFolder = true
     override val supportsSearchByDate = true
     override val isPushCapable = true
-    override val isDeleteMoveToTrash = true
 
     override fun refreshFolderList() {
         commandRefreshFolderList.refreshFolderList()

backend/jmap/src/main/java/com/fsck/k9/backend/jmap/JmapBackend.kt

@@ -39,7 +39,6 @@ class JmapBackend(
     override val supportsTrashFolder = true
     override val supportsSearchByDate = true
     override val isPushCapable = false // FIXME
-    override val isDeleteMoveToTrash = true
 
     override fun refreshFolderList() {
         commandRefreshFolderList.refreshFolderList()

backend/pop3/src/main/java/com/fsck/k9/backend/pop3/Pop3Backend.kt

@@ -32,7 +32,6 @@ class Pop3Backend(
     override val supportsTrashFolder = false
     override val supportsSearchByDate = false
     override val isPushCapable = false
-    override val isDeleteMoveToTrash = false
 
     override fun refreshFolderList() {
         commandRefreshFolderList.refreshFolderList()

backend/webdav/src/main/java/com/fsck/k9/backend/webdav/WebDavBackend.kt

@@ -34,7 +34,6 @@ class WebDavBackend(
     override val supportsTrashFolder = true
     override val supportsSearchByDate = false
     override val isPushCapable = false
-    override val isDeleteMoveToTrash = true
 
     override fun refreshFolderList() {
         commandGetFolders.refreshFolderList()