Deprecate RecorderContext#classProxy method

[jaikiran]

As discussed in the Quarkus dev mailing list, the RecorderContext#classProxy is no longer needed since the build steps can now safely load the application/deployment classes without the need for this proxy construct.

This PR has 3 commits - one which does the deprecation and a couple of others which remove the usage of classProxy from qute and smallrye-health extensions. The updates to qute and smallrye-health are here to make sure things do actually work fine if the usage of classProxy method is replaced. If this shows no regressions, then as separate PRs we can move some of the remaining extensions in this repo, away from this method.

[jaikiran]

The failures so far are unrelated to this change. The one in ConcurrentExecutionTest is being tracked here #10444.
The other failures are in KafkaCodecTest which is failing with:

2020-07-03T03:35:22.1095830Z Caused by: java.lang.RuntimeException: java.lang.IllegalArgumentException: Could not find a 'KafkaServer' or 'client.KafkaServer' entry in the JAAS configuration. System property 'java.security.auth.login.config' is /home/runner/work/quarkus/quarkus/integration-tests/kafka/target/kafka-server-jaas.18011188515337623419.conf
2020-07-03T03:35:22.1096049Z 	at io.quarkus.it.kafka.KafkaSASLTestResource.start(KafkaSASLTestResource.java:46)
2020-07-03T03:35:22.1096219Z 	at io.quarkus.test.common.TestResourceManager.start(TestResourceManager.java:52)
2020-07-03T03:35:22.1096368Z 	... 45 more
2020-07-03T03:35:22.1541184Z Caused by: java.lang.IllegalArgumentException: Could not find a 'KafkaServer' or 'client.KafkaServer' entry in the JAAS configuration. System property 'java.security.auth.login.config' is /home/runner/work/quarkus/quarkus/integration-tests/kafka/target/kafka-server-jaas.18011188515337623419.conf
2020-07-03T03:35:22.1541844Z 	at org.apache.kafka.common.security.JaasContext.defaultContext(JaasContext.java:133)
2020-07-03T03:35:22.1542375Z 	at org.apache.kafka.common.security.JaasContext.load(JaasContext.java:98)
2020-07-03T03:35:22.1542594Z 	at org.apache.kafka.common.security.JaasContext.loadServerContext(JaasContext.java:70)
2020-07-03T03:35:22.1542773Z 	at 

Not yet sure what changed in that area recently.

[Sanne]

Great, thanks @jaikiran !

[jaikiran]

The other failures are in KafkaCodecTest

I created #10469 to track this.