efi: Remove unused extern declaration efi_lookup_mapped_addr()

Since commit 50a0cb56 ("x86/efi-bgrt: Fix kernel panic when mapping BGRT data")
this extern declaration is not used anymore.
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

include/linux/efi.h

@@ -726,7 +726,6 @@ static inline efi_status_t efi_query_variable_store(u32 attributes,
 	return EFI_SUCCESS;
 }
 #endif
-extern void __iomem *efi_lookup_mapped_addr(u64 phys_addr);
 
 extern int __init __efi_memmap_init(struct efi_memory_map_data *data);
 extern int __init efi_memmap_init_early(struct efi_memory_map_data *data);