configurator: Replace unlink with remove

Although Windows provides unlink, using it adds complication due to the
lack of unistd.h which must be included to define the function on POSIX
systems.  Instead, use remove, which C89 requires to be in stdio.h.

Signed-off-by: Kevin Locke <kevin@kevinlocke.name>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>