IDE-284 Change resource download server and links

[Frajhamster]

Jira ticket: https://catrobat.atlassian.net/browse/IDE-284

Description:

• Changed assets/resources download server links
• Removed old unused related code
• A few lines of old code still remains, but should be deleted when the share server completely closes
• Adapted tests

Your checklist for this pull request

Please review the contributing guidelines and wiki pages of this repository.

• Include the name of the Jira ticket in the PR’s title
• Include a summary of the changes plus the relevant context
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• Verify to commit no other files than the intentionally changed ones
• Include reasonable and readable tests verifying the added or changed behavior
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[urkat]

lgtm

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[reichli]

Looks good! Thank you :)