Revert to once again use the legacy build system.

Tulsi breaks with the new build system in Xcode 10.2 (beta) since
it requires a codesigning identity to be present. If we disable codesigning,
then injected test frameworks are not signed properly since Xcode injects them
after running Tulsi's scripts.

PiperOrigin-RevId: 234837165
diff --git a/src/TulsiGenerator/XcodeProjectGenerator.swift b/src/TulsiGenerator/XcodeProjectGenerator.swift
index c2b3b05..8be6a37 100644
--- a/src/TulsiGenerator/XcodeProjectGenerator.swift
+++ b/src/TulsiGenerator/XcodeProjectGenerator.swift
@@ -559,6 +559,7 @@
 
     let workspaceSharedDataURL = projectURL.appendingPathComponent("project.xcworkspace/xcshareddata")
     let sharedWorkspaceSettings: [String: Any] = [
+      "BuildSystemType": "Original",
       "IDEWorkspaceSharedSettings_AutocreateContextsIfNeeded": false as AnyObject,
     ]
     try writeWorkspaceSettings(sharedWorkspaceSettings,