Don't need this constant anymore

Author: grynspan

Package.swift

@@ -477,7 +477,6 @@ extension Array where Element == PackageDescription.CXXSetting {
     } else if let gitHubSHA = Context.environment["GITHUB_SHA"] {
       // When building in GitHub Actions, the git command may fail to get us the
       // commit hash, so check if GitHub shared it with us instead.
-      result.append(.define("SWT_TESTING_LIBRARY_VERSION", to: "0"))
       result.append(.define("SWT_TESTING_LIBRARY_COMMIT_HASH", to: #""\#(gitHubSHA)""#))
     }