Remove 'S' files from watchOS target in CocoaPods

[daltonclaybrook]

SwiftNIOSSL currently fails app store validation when rebuilding from Bitcode due to the presence of the assembly files. While it isn't currently possible to remove these files from SwiftPM-built targets, we can remove them from CocoaPods targets. As such, I believe the podspec should be updated to remove these files from watchOS and the latest version redeployed to the CocoaPods spec repo. This will enable a workaround for watchOS projects until SwiftPM adds the necessary support.

More context in #251