Bootstrap reloading of webfiles performs unnecessary and undesired intermediate removal of existing webfile bundle

On execution of the repository bootstrap WebFileBundleInstruction, before a reload of an existing webfiles bundle the bundle node is first deleted and the session saved, before the PostStartupTask is returned which will eventually (after the normal startup tasks) invoke the WebFilesServiceImpl to import the new webfiles bundle.

As result there is (now, after the session save was added after the initial implementation) some time window during which the existing webfiles bundle no longer is available.
If the current bootstap (upgrade) is done on a cluster of multiple repository instances, other active/running instances therefore might temporarily fail serving the (old) webfiles bundle resources.

However, this 'pre-emptive' delete of the existing webfiles bundle actually isn't needed: the WebFilesServiceImpl will also first remove existing webfiles bundle resources before importing the new bundle.
Furthermore WebFilesServiceImpl itself will not do a session save thus the delete + import of the new bundle is effected as a single change from the PostStartupTask at the end.

Dropping the pre-emptive webfiles bundle delete in WebFileBundleInstruction therefore will fix the temporary unavailability of the webfiles bundle on other active repository instances.