This ABI is moved to /sys/firmware/opal/mpipl/release_core.

What:		/sys/kernel/fadump_release_opalcore
Date:		Sep 2019
Contact:	linuxppc-dev@lists.ozlabs.org
Description:	write only
		The sysfs file is available when the system is booted to
		collect the dump on OPAL based machine. It used to release
		the memory used to collect the opalcore.