[xcodegen] Avoid tracking inferArgs per target/source

This is unnecessary since we never configure it
per target, just check the global setting.

utils/swift-xcodegen/Sources/SwiftXcodeGen/Generator/ProjectSpec.swift

@@ -206,9 +206,7 @@ extension ProjectSpec {
     guard let path = mapPath(path, for: "Clang target") else { return }
     let name = name ?? path.fileName
     clangTargetSources.append(ClangTargetSource(
-      at: path, named: name,
-      mayHaveUnbuildableFiles: mayHaveUnbuildableFiles,
-      inferArgs: inferArgs
+      at: path, named: name, mayHaveUnbuildableFiles: mayHaveUnbuildableFiles
     ))
   }