Bug 35428: Remove temporary files for gulp po tasks

gulp po:update will generate 1 /tmp/koha-* directory per task.

We need to remove them when the script does not longer need them.

Test plan:
0. Do not apply this patch
1. ls -ltr /tmp
2. gulp po:update --lang es-ES
3. ls -ltr /tmp
=> Notice new koha-* directories
Repeat 2, 3
4. Apply this patch and try again
=> No new directories when the job is done

Signed-off-by: David Nind <david@davidnind.com>

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit ba7b62d1fc)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>

gulpfile.js

@@ -386,6 +386,7 @@ function xgettext (cmd, filename) {
                         file.contents = data;
                         callback(null, file);
                     });
+                    fs.rmSync(folder, { recursive: true });
                 });
             });
         })