German: redundant dot 6 in front of closing square bracket

[bertfrees]

Reported by Marcel Bothe from blista:

If there is a single standing letter within square brackets (e.g. "[W]") directly followed by another letter, Liblouis generates an unnecessary second dot 6 in front of the closing square bracket.

display: tables/de-eurobrl6.dis
table: tables/de-g0.utb
tests:
  - - "[W]ährend"
    - "'=w'=`hrend"
    - xfail: "current output is: '=w''=`hrend"
table: tables/de-g1.ctb
tests:
  - - "[W]ährend"
    - "'=w'=`hrend"
    - xfail: "current output is: '=w''=`hrend"
table: tables/de-g2.ctb
tests:
  - - "[W]ährend"
    - "'=w'=`hrcd"
    - xfail: "current output is: '=w''=`hrcd"