[clang-reorder-fields] Fix unused private field warning (NFC)

Fixes:
```
In file included from /home/gha/actions-runner/_work/llvm-project/llvm-project/clang-tools-extra/clang-reorder-fields/Designator.cpp:15:
/home/gha/actions-runner/_work/llvm-project/llvm-project/clang-tools-extra/clang-reorder-fields/Designator.h:157:23: error: private field 'ILE' is not used [-Werror,-Wunused-private-field]
157 |   const InitListExpr *ILE;
```

Author: nikic

clang-tools-extra/clang-reorder-fields/Designator.cpp

@@ -62,7 +62,7 @@ bool Designator::isFinished() {
 
 Designators::Designators(const Expr *Init, const InitListExpr *ILE,
                          const ASTContext *Context)
-    : ILE(ILE), Context(Context) {
+    : Context(Context) {
   if (ILE->getType()->isArrayType()) {
     const ConstantArrayType *CAT =
         Context->getAsConstantArrayType(ILE->getType());
@@ -90,7 +90,7 @@ Designators::Designators(const Expr *Init, const InitListExpr *ILE,
 
 Designators::Designators(const DesignatedInitExpr *DIE, const InitListExpr *ILE,
                          const ASTContext *Context)
-    : ILE(ILE), Context(Context) {
+    : Context(Context) {
   for (const auto &D : DIE->designators()) {
     if (D.isFieldDesignator()) {
       RecordDecl *DesignatorRecord = D.getFieldDecl()->getParent();

clang-tools-extra/clang-reorder-fields/Designator.h

@@ -154,7 +154,6 @@ class Designators {
   /// expression is found.
   bool enterImplicitInitLists(const Expr *Init);
 
-  const InitListExpr *ILE;
   const ASTContext *Context;
   SmallVector<Designator, 1> DesignatorList;
 };