[TableGen] Remove unnecessary includes (NFC)

Identified with clangd.

Author: kazutakahirata

llvm/include/llvm/TableGen/Parser.h

@@ -13,9 +13,6 @@
 #ifndef LLVM_TABLEGEN_PARSER_H
 #define LLVM_TABLEGEN_PARSER_H
 
-#include "llvm/ADT/STLExtras.h"
-#include <vector>
-
 namespace llvm {
 class RecordKeeper;
 class SourceMgr;