Fix the "delete" button in the table view

In c7fa6c8b the code using
`updateFlatStatus` moved to the new file `flatstableline.vue` but the
actual method wasn't moved in the process, yielding an error when one
wanted to use the button.

This patch moves the method to the new file.
4 jobs for fix-delete-button-on-main-table-view in 6 minutes and 40 seconds (queued for 2 seconds)