init: add an init_unlink helper

Add a simple helper to unlink with a kernel space file name and switch
the early init code over to it.  Remove the now unused ksys_unlink.

Signed-off-by: Christoph Hellwig <hch@lst.de>
diff --git a/init/do_mounts_rd.c b/init/do_mounts_rd.c
index d4255c1..ac021ae 100644
--- a/init/do_mounts_rd.c
+++ b/init/do_mounts_rd.c
@@ -272,7 +272,7 @@ int __init rd_load_image(char *from)
 	fput(out_file);
 out:
 	kfree(buf);
-	ksys_unlink("/dev/ram");
+	init_unlink("/dev/ram");
 	return res;
 }