[nrf fromtree] samples: settings: cleanup and use filters

Almost all overlays only enable NVS and SETTINGS_NVS, something that
should be enabled in sample directly. Remove all overlays and make the
sample more genenric.

Use filter on storage partition to enable testing the sample on more
plaforms.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>

Signed-off-by: Sebastian Głąb <sebastian.glab@nordicsemi.no>
(cherry picked from commit 270c4e4)

Author: nordic-segl