g10: Simplify "factory-reset" procedure.

* g10/card-util.c (factory_reset): Simplify.

In this summer, I got report about old code before this change didn't
work with newer Yubikey. I got another report test version of OpenPGP
card V3.3 implementation didn't work, either. Then, I confirmed that
according to the OpenPGP card specification, the procedure of old code
is not expected by its author.

This change simplify "factory-reset" as simple.

Only versions of Gnuk 1.2.2, 1.2.3, 1.2.4, won't work with this
change. That's because the factory-reset feature of Gnuk was
introduced by reading the implementation of GnuPG, instead of reading
the specification. Gnuk 1.2.5 and later works well. All OpenPGPcard
implementations I have work well (2.0, 2.1, 2.2, test version of 3).

• GnuPG-bug-id: T3286
• Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>