devel branch FTBFS since Enigmail 2:2.0.8-5~deb9u1 reached Stretch

Since the Stretch 9.6 point release:

07:19:54 patching file usr/share/xul-ext/enigmail/install.rdf
07:19:54 Reversed (or previously applied) patch detected!  Assume -R? [n] 
07:19:54 Apply anyway? [n] 
07:19:54 Skipping patch.
07:19:54 1 out of 1 hunk ignored -- saving rejects to file usr/share/xul-ext/enigmail/install.rdf.rej

Feature Branch: bugfix/16120-delete-obsolete-enigmail-patch

Related issues

• Related to #15657 (closed)
• Blocks #15506 (closed)

Original created by @intrigeri on 16120 (Redmine)