We currently don't have any convenient means of detecting what packages and TFMs from SBRP are no longer referenced and should be removed. We should have automated reporting/tooling around this.

Reasons this tooling is valuable:

1. Size of SBRP -
   1. Repo size on disk - 5.8 GB
   2. Artifacts size - 119 MB ~10% of all SB artifacts
2. Build times - building fewer packages and tfms will have a direct impact
3. Generate tooling - The tooling to support all possible package versions/TFMs is complicated. Eliminating unnecessary packages/TFMs simplifies this process - e.g. support 4.* TFMs is very different than netstandard/netcore TFMs.