Fix invalid US Government connector list links in whitepapers/power-plat-d365-architecture/README.md

[gretchunkim]

Issue

The README.md currently lists connectors for US Government, but all hyperlinks provided are invalid. This is misleading to users looking references.

• GCC Power Platform Connectors List
• GCC High Power Platform Connectors List
• DOD Power Platform Connectors List

Request

• Update the hyperlinks in the connectors section to the correct, valid links if available.
• If valid links cannot be found for certain connectors, delete the entire connectors section from the README as these resources are unavailable publicly.