This is more consistent with what we do with other similar XML lists,
and avoids a potential confusion with the library-list XML list.
gdb/ChangeLog:
* features/library-list-aix.dtd: Replace library-list by
library-list-aix.
* rs6000-nat.c: Replace library-list by library-list-aix
throughout.
* solib-aix.c: Likewise.