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

[denny-msft]

Started investigating the crash from #1370 and realized that ODWReachability should only be applicable for platforms below iOS 11 and macOS 10.14. However, a crash stack from an iOS 18 device clearly shows these classes being deallocated.

-[ODWReachability stopNotifier] ODWReachability.m:367
-[ODWReachability dealloc] ODWReachability.m:265
Microsoft::Applications::Events::PlatformAbstraction::NetworkInformation::~NetworkInformation() NetworkInformationImpl.mm:102

Seems like there was a bug where these reachability classes were being initialized without guarded availability checks (see NetworkInformation::SetupNetDetect:108) when they should only be used for lower platforms.

Regardless, given the EOL of these versions, this PR remove references to ODWReachability and fixes the crash.

Testing

Verified with build-ios.sh.