Remove ODWReachability and iOS 11 macOS 10.14 code with EOL for those platforms#1371

denny-msft wants to merge 4 commits intomainmicrosoft/cpp_client_telemetry:mainfrom

dennykim/remove-outdated-ios-reachabilitymicrosoft/cpp_client_telemetry:dennykim/remove-outdated-ios-reachabilityCopy head branch name to clipboard