[REF] mail: remove account.move.line hack

While refactoring the move_line_list_views.js in owl, we provided the
account.move id and model + "generate" a thread in the front-end for
account.move.line instead of only providing account.move.line model and id.

This allows us to get rid of this hacky special case

Task-id: 2857743
Part-of: odoo/odoo#96672

addons/account/views/account_move_views.xml

@@ -189,6 +189,7 @@
                     <field name="amount_residual" sum="Total Residual" string="Residual" optional="hide" attrs="{'invisible':[('is_account_reconcile', '=', False)]}"/>
                     <field name="amount_residual_currency" sum="Total Residual in Currency" string="Residual in Currency" optional="hide" attrs="{'invisible':['|', ('is_same_currency', '=', True), ('is_account_reconcile', '=', False)]}"/>
 
+                    <field name="move_id" invisible="1"/>
                     <field name="parent_state" invisible="1"/>
                     <field name="account_type" invisible="1"/>
                     <field name="statement_id" invisible="1"/>

addons/mail/static/src/models/thread.js

@@ -949,10 +949,6 @@ registerModel({
          */
         async setMainAttachment(attachment) {
             this.update({ mainAttachment: attachment });
-            if (this.model === 'account.move.line') {
-                // account.move.line is not actually a thread in python
-                return;
-            }
             await this.messaging.rpc({
                 model: 'ir.attachment',
                 method: 'register_as_main_attachment',

addons/mail/static/src/models/web_client_view_attachment_view.js

@@ -37,11 +37,6 @@ registerModel({
          * @private
          */
         _onChangeThreadAttachmentsInWebClientView() {
-            if (this.thread.model === 'account.move.line') {
-                // account.move.line is not actually a thread in python
-                this.setMainAttachmentFromIndex(0);
-                return;
-            }
             if (
                 this.thread.areAttachmentsLoaded &&
                 !this.thread.isLoadingAttachments &&