Bug 4281: Reports dictionary supports only 1 field selection

Bug 4281: Reports dictionary supports only 1 field selection

The reports dictionary allows the user to select several fields, but
only 1 is used.
The interface is quite confusing.
This patch removes the multiple selection and permit to select only 1
field.

Test plan:
1/ Create a report dictionary (reports/dictionary.pl)
2/ On the step 3, confirm that only 1 field can be selected

Confirm there is no regression on this tool.

Signed-off-by: Nick Clemens <nick@quecheelibrary.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>