Fix files table to only remove row from state after mutation succeeds

[mddilley]

When deleting a row from the files table, Rose caught that the state update is happening before the delete mutation succeeds. See cityofaustin/atd-moped#1521 (comment)

To reproduce:

1. Go to a project's files table with files (like project 290 in a production snapshot) or add some files
2. Use your browser dev tools to set your connection to "Offline"
3. Delete a file and see that an error snackbar appears but the row has already deleted from the table state even though the mutation failed