Update template version constraints

Once https://github.com/phpDocumentor/UnifiedAssetInstaller/pull/3 has been merged and tagged, and also all the phpDocumentor templates have had their corresponding pull requests merged and tagged this will be good to go.

I have not adjusted the constraints for "phpdocumentor/template-clean" as it is still in beta.

The dependency on "phpdocumentor/unified-asset-installer" has been removed as phpDocumentor does
not directly depend on it.