Remove unnecessary dispatch_async

Session/Signal/ConversationView/ConversationViewController.m

@@ -3738,8 +3738,7 @@ typedef enum : NSUInteger {
     [self.conversationViewModel appendUnsavedOutgoingTextMessage:tsMessage];
     [LKStorage writeWithBlock:^(YapDatabaseReadWriteTransaction *transaction) {
         message.linkPreview = [SNLinkPreview from:linkPreviewDraft using:transaction];
-    } completion:^{
-        dispatch_async(dispatch_get_main_queue(), ^{
+    } completion:^{ // Completes on the main queue
         tsMessage.linkPreview = [OWSLinkPreview from:message.linkPreview];
         [LKStorage writeWithBlock:^(YapDatabaseReadWriteTransaction *transaction) {
             [tsMessage saveWithTransaction:transaction];
@@ -3754,7 +3753,6 @@ typedef enum : NSUInteger {
         dispatch_async(dispatch_get_main_queue(), ^{
             [[weakSelf inputToolbar] toggleDefaultKeyboard];
         });
-        });
     }];
 }