[FIX] remove unnecessary local, convert set to indexedseq

By default "iterating" a set will use a setseq which may still uniquify
information if it finds duplicates (but it may not as it's lazy &
al). #flatten conserves the seq type, so if there are two equal
operation items amongst all selected operations they may get
deduplicated, with the end result of operations disappearing in the
final formatted result.

_static/chart-of-accounts.js

@@ -99,10 +99,9 @@
             );
         },
         accounts: function() {
-            var _this = this;
             var data = this.props.p.get('operations');
 
-            var totals = data.flatten(true).reduce(function (acc, op) {
+            var totals = data.toIndexedSeq().flatten(true).reduce(function (acc, op) {
                 return acc
                     .updateIn([op.get('account'), 'debit'], function (d) {
                         return (d || 0) + op.get('debit', zero)(data);