[TASK] Drop `app-dir` from `composer.json`

[oliverklee]

Fixes #1744

[coveralls]

Pull Request Test Coverage Report for Build 9141570369

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.444%

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Totals
Change from base Build 9141555074:	0.0%
Covered Lines:	1734
Relevant Lines:	1836

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💛 - Coveralls