remove qcow2 and virtualbox disk image

nobody should use them, because it's insecure.
7 jobs for master in 22 seconds (queued for 261 minutes and 51 seconds)
latest
Status Name Job ID Coverage
  Lint
passed flake8 #2178

00:00:20

passed shellcheck #2175

00:00:17

passed shfmt #2176

00:00:13

passed validate-packer #2179

00:00:18

passed yapf #2177

00:00:14

 
  Build
failed build:qemu #2180
secure-kvm

failed build:virtualbox #2181
secure-virtualbox

 
Name Stage Failure
failed
build:virtualbox Build There has been a timeout failure or the job got stuck. Check your timeout limits or try again
No job log
failed
build:qemu Build There has been a timeout failure or the job got stuck. Check your timeout limits or try again
No job log