Merge pull request #1228 from rintaro/remove-syntaxtree

Remove legacy libSyntax related options

Author: rintaro

Sources/SwiftDriver/Driver/Driver.swift

@@ -1901,7 +1901,7 @@ extension Driver {
       case .indexFile:
         compilerOutputType = .indexData
 
-      case .parse, .resolveImports, .typecheck, .dumpParse, .emitSyntax,
+      case .parse, .resolveImports, .typecheck, .dumpParse,
            .printAst, .dumpTypeRefinementContexts, .dumpScopeMaps,
            .dumpInterfaceHash, .dumpTypeInfo, .verifyDebugInfo:
         compilerOutputType = nil