Remove `swiftLanguageVersions` from Package.swift
Remove `swiftLanguageVersions` from Package.swift

https://github.com/apple/swift-package-manager/blob/master/Documentation/PackageDescriptionV4.md#swiftlanguageversions
> If a package does not specify any Swift language versions, the language version to be used will match the major version of the package's Swift tools version.

jpsim/Yams,jpsim/Yams,jpsim/Yams