[IMP] mail: remove useless 't-ref="dropzone"'

Task-2694206

Part-of: odoo/odoo#81801

addons/mail/static/src/component_hooks/use_drag_visible_dropzone/use_drag_visible_dropzone.js

@@ -4,8 +4,6 @@ const { useState, onMounted, onWillUnmount } = owl.hooks;
 
 /**
  * This hook handle the visibility of the dropzone based on drag & drop events.
- * It needs a ref to a dropzone, so you need to specify a t-ref="dropzone" in
- * the template of your component.
  *
  * @returns {Object}
  */

addons/mail/static/src/components/attachment_box/attachment_box.xml

@@ -16,7 +16,6 @@
                         <DropZone
                             className="'o_AttachmentBox_dropZone'"
                             onDropzoneFilesDropped="_onDropZoneFilesDropped"
-                            t-ref="dropzone"
                         />
                     </t>
                     <t t-if="attachmentBoxView.chatter.attachmentList">

addons/mail/static/src/components/composer/composer.xml

@@ -21,7 +21,6 @@
                     <DropZone
                         className="'o_Composer_dropZone'"
                         onDropzoneFilesDropped="_onDropZoneFilesDropped"
-                        t-ref="dropzone"
                     />
                 </t>
                 <FileUploader localId="composerView.fileUploaderView.localId"/>