Revert "programming-guide-pstore: Update doc"

During tests on SabreLite board, I found that the memory isn't reserved for the Ramoops backend from parameters added in the Device Tree by U-boot.
Revert this commit until a proper fix has been found.

This reverts commit f1c1d650.

Signed-off-by: Frédéric Danis frederic.danis@collabora.com