powerpc/64s/tlbflush-radix: Remove unused radix__flush_tlb_pwc()

powerpc/64s/tlbflush-radix: Remove unused radix__flush_tlb_pwc()

Commit 52162ec784fa
("powerpc/mm/book3s64/radix: Use freed_tables instead of need_flush_all")
removed radix__flush_tlb_pwc() definition, but missed to remove the extern
declaration. This patch removes it.

Reviewed-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/b79c8ce8f00aa3e96ab9b1c77bc004759c397d3f.1773078178.git.ritesh.list@gmail.com