Remove deprecated dnsResolver option (#3328)

[The-East-Wind]

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• Part of Remove deprecated options and logic as part of the 7.0 release #3328 (completely remove the dnsResolver option)
• Follows up Deprecate lettuce DNS support classes  #1527

Changes

1. Removed usages of ClientResources#dnsResolver
2. Removed ClientResources#dnsResolver and all of it's implementations in DefaultClientResources
3. Removed redundant classes which are no longer relevant
4. Removed deprecated JVM_DEFAULT DnsResolver
5. Fixed failing tests

Followup questions for maintainers

1. Should DnsResolver and it's implementations be removed or should they continue to exist
2. If DnsResolver is to be removed should SockerAddressResolver make direct use of netty's AddressResolverGroup