cachefiles: remove unneeded include of <linux/fdtable.h>

close_fd() has been killed, let's get rid of unneeded
<linux/fdtable.h> as Al Viro pointed out [1].

[1] https://lore.kernel.org/r/20240603034055.GI1629371@ZenIV

Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20240603062344.818290-1-hsiangkao@linux.alibaba.com
Signed-off-by: Christian Brauner <brauner@kernel.org>