Reverts "Implement dartPluginClass support for plugins #74469" (#78623)

* Revert "Enable dart_plugin_registry_test (#76645)"

This reverts commit 109e0bb9f55ed6e9884547843356d16897eaf6a9.

* Revert "Apply changes caused by https://github.com/flutter/flutter/pull/76662 (#77093)"

This reverts commit cdca6485f05287bb12b1acebbbae2ba107d6c1be.

* Revert "Disable clang format in the plugin registrants (#76662)"

This reverts commit dadbd47d097f5cce868832fa8b4d03439a5c8402.

* Revert "Disable warnings for the dart plugin registrant (#76561)"

This reverts commit 098ece522d41f25370d19f5ec09d93ce2e727019.

* Revert "Remove dart_plugin_registry_test timeouts (#76838)"

This reverts commit 1610a2747654dec3cabbd1d81d0bc5885b2067a2.

* Revert "Implement dartPluginClass support for plugins (#74469)"

This reverts commit b7d4806243a4e906bf061f79a0e314ba28111aa6.

Kick.