refactor: clean up retired feature flags

[jayzhang]

https://msazure.visualstudio.com/Microsoft%20Teams%20Extensibility/_workitems/edit/27732037

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 87.74%. Comparing base (ded43fb) to head (6cf8636).

Additional details and impacted files

[](https://app.codecov.io/gh/OfficeDev/TeamsFx/pull/11414?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OfficeDev) ```diff @@ Coverage Diff @@ ## dev #11414 +/- ## ========================================== - Coverage 87.75% 87.74% -0.01% ========================================== Files 493 493 Lines 29471 29444 -27 Branches 5683 5855 +172 ========================================== - Hits 25862 25836 -26 + Misses 1777 1776 -1 Partials 1832 1832 ``` | [Files](https://app.codecov.io/gh/OfficeDev/TeamsFx/pull/11414?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OfficeDev) | Coverage Δ | | |---|---|---| | [packages/fx-core/src/common/constants.ts](https://app.codecov.io/gh/OfficeDev/TeamsFx/pull/11414?src=pr&el=tree&filepath=packages%2Ffx-core%2Fsrc%2Fcommon%2Fconstants.ts&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OfficeDev#diff-cGFja2FnZXMvZngtY29yZS9zcmMvY29tbW9uL2NvbnN0YW50cy50cw==) | `100.00% <ø> (ø)` | | | [packages/fx-core/src/common/featureFlags.ts](https://app.codecov.io/gh/OfficeDev/TeamsFx/pull/11414?src=pr&el=tree&filepath=packages%2Ffx-core%2Fsrc%2Fcommon%2FfeatureFlags.ts&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OfficeDev#diff-cGFja2FnZXMvZngtY29yZS9zcmMvY29tbW9uL2ZlYXR1cmVGbGFncy50cw==) | `98.14% <100.00%> (+1.17%)` | :arrow_up: |