Remove SupportTestingClient interface

[manusa]

Removal of SupportTestingClient interface

@manusa in the last meeting we talked about whether it would make more sense here just to go ahead and remove the deprecated isAdaptable and all of these checks from the extensions. Would you rather that be a follow-on task instead?

Originally posted by @shawkins in #4631 (comment)

[shawkins]

• Step 1 - remove isAdaptable and SupportTestingClient from the extension impls.
• Step 2 - consider deprecating SupportTestingClient / isSupported - if we don't think this style of support testing makes sense moving forward. It was brought up that for even the OpenShiftClient it's kind of dubious. fix #4659: deprecating support testing client #4869
• Step 3 - later remove SupportTestingClient.

[manusa]

Affects:

• KnativeDeployer environment check is breaking the build quarkusio/quarkus#28171
• Fix Knative/OpenShift client environment check quarkusio/quarkus#28172
• Remove workaround for testing knative environment quarkusio/quarkus#30743

[stale]

This issue has been automatically marked as stale because it has not had any activity since 90 days. It will be closed if no further activity occurs within 7 days. Thank you for your contributions!