ecryptfs: remove version_str file from sysfs

This file violates the one-value-per-file sysfs rule.

If you all want it added back, please do something like a per-feature
file to show what is present and what isn't.

Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Mike Halcrow <mhalcrow@us.ibm.com>
Cc: Phillip Hellewell <phillip@hellewell.homeip.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>