init: add an init_rmdir helper

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

Signed-off-by: Christoph Hellwig <hch@lst.de>

fs/init.c

@@ -42,3 +42,8 @@ int __init init_unlink(const char *pathname)
 {
 	return do_unlinkat(AT_FDCWD, getname_kernel(pathname));
 }
+
+int __init init_rmdir(const char *pathname)
+{
+	return do_rmdir(AT_FDCWD, getname_kernel(pathname));
+}