Deleted overridden shadow tiddlers on language change.

I am trying to understand why are there `enqueueTiddlerEvent` calls for shadow tiddlers.

I have an issue concerning automatically deleted overridden shadow tiddlers on language change.

Way to reproduce:
* start `tiddlywiki mywiki --server`
```
"TiddlyWebAdaptor:" "Getting status"
"TiddlyWebAdaptor:" "Status:" "{"space":{"recipe":"default"},"tiddlywiki_version":"5.1.5-prerelease"}"
"syncer-browser:" "Retrieving skinny tiddler list"
```
* *Language is English (British) by default*
* Set `$:/SiteTitle` to `Whatever`
```
"syncer-browser:" "Dispatching 'save' task:" "$:/SiteTitle"
"syncer-browser:" "Retrieving skinny tiddler list"
```
* Set language to e.g. Russian
```
"syncer-browser:" "Dispatching 'save' task:" "$:/language"
"syncer-browser:" "Dispatching 'save' task:" "$:/SiteTitle"
"syncer-browser:" "Retrieving skinny tiddler list"
```
* Set language back into English
```
"syncer-browser:" "Dispatching 'delete' task:" "$:/SiteTitle"
"syncer-browser:" "Dispatching 'save' task:" "$:/language"
```
* Hit F5 and `$:/SiteTitle` is lost forever

After modification - same actions:
```
"TiddlyWebAdaptor:" "Getting status"
"TiddlyWebAdaptor:" "Status:" "{"space":{"recipe":"default"},"tiddlywiki_version":"5.1.5-prerelease"}"
"syncer-browser:" "Retrieving skinny tiddler list"
"syncer-browser:" "Dispatching 'save' task:" "$:/SiteTitle"
"syncer-browser:" "Retrieving skinny tiddler list"
"syncer-browser:" "Dispatching 'save' task:" "$:/language"
"syncer-browser:" "Retrieving skinny tiddler list"
"syncer-browser:" "Dispatching 'save' task:" "$:/language"
```