Update URLs in source code

[jsiirola]

Fixes # .

Summary/Motivation:

This updates some URLs in the codebase and should get the URL checker passing again.

TODOs (maybe convert to an Issue for a future PR)

• convert remaining http URLS to https
• (manually) verify all URLs; several are now redirecting to uninformative locations

Changes proposed in this PR:

• remove a broken reference to projects.coin-or.org
• remove unnecessary URLs from the COIN-OR projDesc.xml
• Update the link for release downloads
• switch some http -> https

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