Revert "[nrf noup] zephyr: add 'minimal' configuration files"

This reverts commit 54f2129.

nrf-squash! [nrf noup] zephyr: add 'minimal' configuration files

The minimal configuration is now deprecated:
- it is not minimal configuration anymore
- built image cannot fit into flash memory
- smp_svr_mini_boot sample is a new reference for minimal config

Signed-off-by: Adam Szczygieł <adam.szczygiel@nordicsemi.no>

Author: adsz-nordic