Revert "[Dependency Scanning] Restore passing external target map as inputs to the scanning action."

Author: artemcm

Sources/SwiftDriver/ExplicitModuleBuilds/ModuleDependencyScanning.swift

@@ -52,37 +52,11 @@ public extension Driver {
                                  moduleDependencyGraphUse: .dependencyScan)
     // FIXME: MSVC runtime flags
 
-    // Pass in external target dependencies to be treated as placeholder dependencies by the scanner
-    if let externalTargetPaths = externalTargetModulePathMap {
-      let dependencyPlaceholderMapFile =
-      try serializeExternalDependencyArtifacts(externalTargetPaths: externalTargetPaths)
-      commandLine.appendFlag("-placeholder-dependency-module-map-file")
-      commandLine.appendPath(dependencyPlaceholderMapFile)
-    }
-
     // Pass on the input files
     commandLine.append(contentsOf: inputFiles.map { .path($0.file) })
     return (inputs, commandLine)
   }
 
-  /// Serialize a map of placeholder (external) dependencies for the dependency scanner.
-   private func serializeExternalDependencyArtifacts(externalTargetPaths: ExternalTargetModulePathMap)
-   throws -> VirtualPath {
-     var placeholderArtifacts: [SwiftModuleArtifactInfo] = []
-     // Explicit external targets
-     for (moduleId, binaryModulePath) in externalTargetPaths {
-       let modPath = TextualVirtualPath(path: VirtualPath.absolute(binaryModulePath).intern())
-       placeholderArtifacts.append(
-           SwiftModuleArtifactInfo(name: moduleId.moduleName,
-                                   modulePath: modPath))
-     }
-     let encoder = JSONEncoder()
-     encoder.outputFormatting = [.prettyPrinted]
-     let contents = try encoder.encode(placeholderArtifacts)
-     return VirtualPath.createUniqueTemporaryFileWithKnownContents(.init("\(moduleOutputInfo.name)-external-modules.json"),
-                                                                   contents)
-   }
-
   /// Returns false if the lib is available and ready to use
   private func initSwiftScanLib() throws -> Bool {
     // If `-nonlib-dependency-scanner` was specified or the libSwiftScan library cannot be found,