Revert "ovl: get_write_access() in truncate"

This reverts commit 03bea604.

Commit 4d0c5ba2 ("vfs: do get_write_access() on upper layer of
overlayfs") makes the writecount checks inside overlayfs superfluous, the
file is already copied up and write access acquired on the upper inode when
ovl_setattr is called with ATTR_SIZE.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>