[caissedepargne] prevent duplicates of conso loans accounts

The xpath in get_real_estate_loans() wasn't accurate enough and also
included consommation loans. They are also fetched in get_loan_list()
causing the duplicates.

Also: the method that tests the existence of loans introduced in
245916d10ee13aeacf996729ddf4d2db629ff004 is being removed because the
new xpath exclude non-relevant HTML elements to be matched and thus the
parsing code to crash (when there is no real estate loans, no element is
returned by the xpath).