[PATCH v3] ntdll: Fix arch heap free.

[Chao Long]

valgrind log:
 2178 ==31639== 4 bytes in 1 blocks are definitely lost in loss record 21 of 457
 2179 ==31639==    at 0x7BC6F0DA: notify_alloc (heap.c:260)
 2180 ==31639==    by 0x7BC731BB: RtlAllocateHeap (heap.c:1725)
 2181 ==31639==    by 0x7BC43A69: xmlstrdupW (actctx.c:747)
 2182 ==31639==    by 0x7BC462EA: parse_assembly_identity_elem (actctx.c:1524)
 2183 ==31639==    by 0x7BC483D9: parse_dependent_assembly_elem (actctx.c:2210)
 2184 ==31639==    by 0x7BC486AE: parse_dependency_elem (actctx.c:2254)
 2185 ==31639==    by 0x7BC49B23: parse_assembly_elem (actctx.c:2681)