hello_bdev: remove passthru section from conf file.

by removing the passthru stuff from the conf file, we create a more
dramatic effect when we add in the passthru bdev during the labs.

Change-Id: I0a0ed101dd4135d8b2774cdd0850ca3bf2e43d01
Signed-off-by: Seth Howell <seth.howell@intel.com>
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/450187


Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>