Delete documentation/API_documentation/NUMBER_VERIFICATION_API.md

[AxelNennker]

The API documentation is now in the yaml file.
To avoid duplication the WG decided to delete this file.

What type of PR is this?

• documentation

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ ACTION	actionlint	2		0	0.03s
✅ OPENAPI	spectral	1		0	1.65s
✅ REPOSITORY	git_diff	yes		no	0.01s
✅ REPOSITORY	secretlint	yes		no	0.72s
✅ YAML	yamllint	1		0	0.32s

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[bigludo7]

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