Remove unnecessary Lexer.h include.

Author: mwyman

lib/Index/Index.cpp

@@ -25,7 +25,6 @@
 #include "swift/Basic/StringExtras.h"
 #include "swift/IDE/SourceEntityWalker.h"
 #include "swift/Markup/Markup.h"
-#include "swift/Parse/Lexer.h"
 #include "swift/Sema/IDETypeChecking.h"
 #include "llvm/ADT/APInt.h"
 #include "llvm/ADT/SmallVector.h"