jobs/buildAll: removed useless statement about cleaning repo

there is no repository to clean in the nightly pipeline.

Signed-off-by: Marc Mattmüller <marc.mattmueller@netmodule.com>

jobs/Jenkinsfile_BuildAll

@@ -260,5 +260,4 @@ def buildAllTargets(commonHelpers, buildBranch) {
       error("Failing build - first machine failing = ${firstMachineFailing}")
     }
   } // end catchError
-  commonHelpers.cleanupRepository("${env.YOCTO_REPO_DIR}")
 }