remove unnecessary casts

[Neil Williams]

Log Message:
-----------
remove unnecessary casts

Tags:
----
gnucash-gnome2-dev

Modified Files:
--------------
    gnucash/src/business/business-core/file:
        gnc-customer-xml-v2.c
        gnc-employee-xml-v2.c
        gnc-job-xml-v2.c
        gnc-order-xml-v2.c
        gnc-tax-table-xml-v2.c