Don't clobber thumbnail url on MXKAttachment

Goes with https://github.com/matrix-org/matrix-ios-kit/pull/191

This might cause a file search view to use larger thumbnails than
it did previously, although I'm not actually sure this is wired up
anywhere. If it is, I'd rather find the place they're used and
switch it to use getThumbnailUrlForSize with the size it wants.

Vector/Model/Search/FilesSearchCellData.m

@@ -34,20 +34,6 @@
 
         roomId = event.roomId;
         
-        // Check attachment if any
-        if ([searchDataSource.eventFormatter isSupportedAttachment:event])
-        {
-            // Note: event.eventType is equal here to MXEventTypeRoomMessage
-            attachment = [[MXKAttachment alloc] initWithEvent:event andMatrixSession:searchDataSource.mxSession];
-            if (attachment && attachment.type == MXKAttachmentTypeImage && attachment.thumbnailURL == nil)
-            {
-                // Suppose contentURL is a matrix content uri, we use SDK to get the well adapted thumbnail from server
-                attachment.thumbnailURL = [searchDataSource.mxSession.matrixRestClient urlOfContentThumbnail:attachment.contentURL
-                                                                                             toFitViewSize:CGSizeMake(73, 73)
-                                                                                                withMethod:MXThumbnailingMethodCrop];
-            }
-        }
-        
         // Title is here the file name stored in event body
         title = [event.content[@"body"] isKindOfClass:[NSString class]] ? event.content[@"body"] : nil;