Bug 30397: Remove duplicate entry from length menu of patrons search

Bug 30397: Remove duplicate entry from length menu of patrons search

If you have 20 in PatronsPerPage, there will be two 20 entries in the
length menu of the patrons search.
jQuery.unique is stupid it seems, it requires the array to be sorted (?)

let x = [1, 2, 1, 2]
jQuery.unique(x);
Array(4) [ 1, 2, 1, 2 ]

x = [1, 1, 2, 2]
jQuery.unique(x);
Array [ 1, 2 ]

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>