Remove deprecated dnsResolver option (#3328)

[The-East-Wind]

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Resolves parts of #3328

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