aiaiai-email-lda: allow reaping of series directories

aiaiai-email-lda: allow reaping of series directories

reap_old did not remove series directories, because "rm -f" does not
remove directories. However, adding just "-r" to the rm command results
in extraneous "directory does not exist" because find will be searching
more than one depth. Change reap_old to have a max depth of 1 so that it
doesn't descend into directories and will happily remove series
directories created inside of queue.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>