This reverts commit 686887e2, now that
<https://gerrit.libreoffice.org/#/c/33186/> "external/firebird: Backport fix for
CORE-5452 causing spurious SEGV" should fix the instability.

Change-Id: I9483c04de36d83233485f1280c3cada84767d696
Reviewed-on: https://gerrit.libreoffice.org/33189Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>