Remove sources with LEGACY STATE from registry

[evantahler]

Slack Thread

From this Mb Query # of Connections active in the last 30 days:
source-talkdesk-explore - 0
source-kustomer-singer - 0
source-courier - 0
source-zuora - 1
source-dv-360 - 0
source-linnworks - 0
source-search-metrics - 0
source-appstore-singer - 0
source-recurly - 7

This PR also coincides with hiding these connectors from Cloud by adding the actors to the connectors.hideActorDefinitionFromList Feature Flag

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[github-actions]

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[evantahler]

Note that this PR also removes these connectors from the OSS repo

[alafanechere]

😢 I supported the merge of this contributed connectors two years ago

[alafanechere]

I think its also safe to remove other singer based connector if any. They're all probably using the LEGACY STATE. And we can remove the generator for singer.

[evantahler]

I think there are only 2 left!

[evantahler]

/approve-and-merge reason="metadata-only changes for connectors whose tests don't pass"

[octavia-approvington]

Check that box