ghcjs: revert "mark build as broken"

This reverts commit 8f07d4bd780a24dcf33be46d8cbfc6163fcdde0e. The build
failure blocking this package has been fixed in the meanwhile. Thanks to
@basvandijk for the heads-up.

(cherry picked from commit 56d033ac1b00a8b29bc29589312d2f5024656bd3)