fix(fs/rmtree): fix huge memory usage (#7073)

Fixes zammad#15258

This adds a sane concurrency limit of 2 per depth level.

Co-authored-by: Florent BEAUCHAMP <florent.beauchamp@vates.fr>

@xen-orchestra/fs/src/abstract.js

@@ -624,14 +624,18 @@ export default class RemoteHandlerAbstract {
 
     const files = await this._list(dir)
     await asyncEach(files, file =>
-      this._unlink(`${dir}/${file}`).catch(error => {
+      this._unlink(`${dir}/${file}`).catch(
+        error => {
           // Unlink dir behavior is not consistent across platforms
           // https://github.com/nodejs/node-v0.x-archive/issues/5791
           if (error.code === 'EISDIR' || error.code === 'EPERM') {
             return this._rmtree(`${dir}/${file}`)
           }
           throw error
-      })
+        },
+       // real unlink concurrency will be 2**max directory depth 
+        { concurrency: 2 }
+      )
     )
     return this._rmtree(dir)
   }