libeigen: update to 3.2.6

It seems that the libeigen patch is not required anymore. I could
not find any issue while building libeigen and other recipes
depending on libeigen.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@oss.bmw-carit.de>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>