[ltp] Dropping thinkpad-acpi backport support for 2.6.20, 2.6.21

[Henrique de Moraes Holschuh]

As I write this, we have very good and very stable 2.6.22.y and 2.6.23.y
kernels, and 2.6.24.y is already out there.

The effort to take care of older branches of thinkpad-acpi is not small, and
the chances that I screw up a backport due to subtle kernel API differences
increases with every new kernel version.

Therefore, I will be dropping 2.6.20 and 2.6.21 from further thinkpad-acpi
releases.

2.6.22 support will continue for a small while yet.

If anyone would like to work on backporting newer thinkpad-acpi patches to
2.6.20 and 2.6.21, you're welcome.  Contact me on the ibm-acpi-devel ML if
that's the case.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh