for aufs: linux-v5.10-rc1, no more vfs_(read|write)f_t

By the commit in v5.10-rc1,
	4d03e3cc

 2020-09-08 fs: don't allow kernel reads and writes without iter ops
every f_op->read() and ->write() are less meaningful.
Now aufs stops using them.

Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
(cherry picked from commit 74fdd92b2332acfbf671b3c4bef5053159492521
 in https://github.com/sfjro/aufs5-linux)
[VB: Remove symbol exports along with the code.]
Signed-off-by: Vefa Bicakci <vefa.bicakci@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>