Move transitional package to to "oldlibs/optional"
This resolves two lintian warnings:
W: notmuch-emacs: transitional-package-should-be-oldlibs-optional oldlibs/extra
W: notmuch-emacs: priority-extra-is-replaced-by-priority-optional
Package: notmuch-emacs
Section: oldlibs
Package: notmuch-emacs
Section: oldlibs
Architecture: all
Depends: elpa-notmuch, ${misc:Depends}
Description: thread-based email index, search and tagging (transitional package)
Architecture: all
Depends: elpa-notmuch, ${misc:Depends}
Description: thread-based email index, search and tagging (transitional package)