ci: Use deleteDir() (non Docker workers) to cleanup workspace directory

We can use deleteDir() at the end of the native stages.
On Windows the cleanup command doesn't work completely,
replace it with the provided Jenkins method. Use it
at the other native CI workers too.

Author: big-r81

build-aux/Jenkinsfile

@@ -358,7 +358,8 @@ def generateNativeStage(platform) {
             finally {
               junit '**/.eunit/*.xml, **/_build/*/lib/couchdbtest/*.xml, **/src/mango/nosetests.xml, **/test/javascript/junit.xml'
               sh 'killall -9 beam.smp || true'
-              sh "${wscleanup()}"
+              // deleteDir is OK here because we're not inside of a Docker container!
+              deleteDir()
             }
           } else {
             //steps to configure and build CouchDB on Windows platforms
@@ -462,7 +463,8 @@ def generateNativeStage(platform) {
                 error("Build step failed with error: ${err.getMessage()}")
               }
               finally {
-                powershell( script: "Remove-Item -Path '${WORKSPACE}\\*' -Force -Recurse -ErrorAction SilentlyContinue")
+                // deleteDir is OK here because we're not inside of a Docker container!
+                deleteDir()
               }
             }
           }