fix(ci)_: drop clean.sh script from cleanup stage

Because it keeps failing due to paths that appear alive but are not.

Signed-off-by: Jakub Sokołowski <jakub@status.im>

ci/tools/Jenkinsfile.nix-cache

@@ -123,7 +123,6 @@ pipeline {
   post {
     always { script {
       nix.shell('nix-store --optimize', pure: false)
-      nix.shell('nix/scripts/clean.sh', pure: false)
     } }
   }
 }