unnecessary line in `define-context-properties.scm`?

[Werner LEMBERG]

I wonder whether line 35 in file `define-context-properties.scm` is
necessary.  AFAICS, the `map` call in functions
`all-user-translation-properties` and
`all-internal-translation-properties`, together with the following

```
(define-public all-translation-properties
  (append all-user-translation-properties
          all-internal-translation-properties))
```

completely construct `all-translation-properties`.  Why the additional
`set!`?


    Werner