[Bug]: Update leaves old files behind (Gameserver detects mismatch)

### Severity

severity: low

### Reproducibility

reproducible: always

### Regression

regression: yes

### Affects latest release

latest-release: yes

### User story

As the updates are automated a check for left behind files should be implemented (or the whole serverfiles except for "data" removed).

### Script name

vintsserver

### Game

Vintage Story

### Linux distro

Ubuntu 24.04

### Command

command: update

### Expected behavior

The server applies updates as expected to the newest version without errors.

### Actual behavior

The update script leaves files from the old version behind which causes errors.

### Further information

The server files (http://api.vintagestory.at/stable-unstable.json) include a specific empty "version-.txt" file. The name differs per version and won't be removed in case of an update via LinuxGSM.
At startup the Vintage Story Server checks for mismatched files and refuses to start.

Manual fix: Cleanup (rm version-.txt) and server restart

### Pre-checks

- [x] I ran update and validate before reporting this issue.

### Relevant log output

```shell
Manual download and diff:
diff -rq vs_server_linux-x64_1.22.1 vs_server_linux-x64_1.22.2 | grep "Only in"
Only in vs_server_linux-x64_1.22.1/assets: version-1.22.1.txt
Only in vs_server_linux-x64_1.22.2/assets: version-1.22.2.txt

[Server Error] Your Server installation still contains old files from a previous game version, which may break things. Please fully delete the /assets folder and then do a full reinstallation. Shutting down server.

ls serverfiles/assets/
creative game gameicon.ico survival version-1.22.1.txt version-1.22.2.txt

LinuxGSM version: v26.1.0
```

### Steps to reproduce

1. Install an older version (e.g. 1.22.1)
2. Update to the newest version
3. Start the server
4. Check the console.log ("Your Server installation still contains old files")
5. Check the serverfiles/assets directory for duplicate version files (version-1.22.1.txt version-1.22.2.txt)