[clang] Remove unused variable 'ExprDependenceBits' in ASTWriterDecl.…

…cpp (NFC)

llvm-project/clang/lib/Serialization/ASTWriterDecl.cpp:2342:12:
 error: unused variable 'ExprDependenceBits' [-Werror,-Wunused-variable]
 2342 |   unsigned ExprDependenceBits = llvm::BitWidth<ExprDependence>;
      |            ^~~~~~~~~~~~~~~~~~
1 error generated.

clang/lib/Serialization/ASTWriterDecl.cpp

@@ -2339,7 +2339,6 @@ void ASTWriter::WriteDeclAbbrevs() {
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));
   DeclCXXMethodAbbrev = Stream.EmitAbbrev(std::move(Abv));
 
-  unsigned ExprDependenceBits = llvm::BitWidth<ExprDependence>;
   // Abbreviation for EXPR_DECL_REF
   Abv = std::make_shared<BitCodeAbbrev>();
   Abv->Add(BitCodeAbbrevOp(serialization::EXPR_DECL_REF));