Remove dependency on plugin-site-api from build

[lemeurherve]

To avoid build failures, and as all plugin data is now available at https://reports.jenkins.io/plugin-site-api/ since jenkins-infra/helpdesk#4976 (comment), builds from this repository should not depend on https://plugins.jenkins.io/api, which is the backend service coming from https://github.com/jenkins-infra/plugin-site-api, and which can be down while https://reports.jenkins.io should be much more reliable.

[saurabhraghuvanshii]

@lemeurherve I want to explore this issue