Should report warning if some one is suppressing a non-existing linter

[ArcturusZhang]

https://github.com/Azure/azure-rest-api-specs/blob/95a0044227b6baad5906c21b0b721f36126bf1fd/specification/translation/Azure.AI.TextTranslation/models-translate.tsp#L152

I think since we redesign the enums and unions, we have removed the linter in typespec-azure-core because I did not search such rules now, then should we report warning when some one tries to suppress a non-existing linter rule?

[timotheeguerin]

I do agree it would be nice to report unused suppresions but it can be tricky. If you suppress something only applying to a specific emitter that is not run we don't want to keep warning about it. Or if the emitter only triggers that warning with some setting on, there is not really a good way to reliably know if the suppression is actually unused.