configs: remove integrator926_defconfig

configs: remove integrator926_defconfig

Remove the integrator926_defconfig configuration, which has not been
updated since a very long time, and targets hardware that is quite
difficult, not to say impossible, to get.

While Qemu has an emulation for the Integrator CP platform, it doesn't
seem to emulate a hard drive, which makes it not very useful. In
addition, we already have the qemu_arm_versatile_defconfig for an
ARMv5 platform emulated in Qemu.

Therefore, let's get rid of this fairly old and never updated
defconfig.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>