[clang] co_return cleanup

[urnathan]

Summary

There's no need for the CoreturnStmt getChildren member to
deal with the presence or absence of the operand member. All
users already deal with null children.

[MaskRay]

LGTM. (I need to learn this stuff but I'm happy since bots are happy:))

clang/include/clang/AST/StmtCXX.h

public:
   void setIsVoid(bool value = true) { IsVoid = value; }
 
   SourceLocation getBeginLoc() const LLVM_READONLY { return CoreturnLoc; }
   SourceLocation getEndLoc() const LLVM_READONLY {
     return getOperand() ? getOperand()->getEndLoc() : getBeginLoc();
   }
 
   child_range children() {
-    if (!getOperand())
-      return child_range(SubStmts + SubStmt::PromiseCall,
-                         SubStmts + SubStmt::Count);
     return child_range(SubStmts, SubStmts + SubStmt::Count);
   }
 
   const_child_range children() const {
-    if (!getOperand())
-      return const_child_range(SubStmts + SubStmt::PromiseCall,
-                               SubStmts + SubStmt::Count);
     return const_child_range(SubStmts, SubStmts + SubStmt::Count);
   }
 
   static bool classof(const Stmt *T) {
     return T->getStmtClass() == CoreturnStmtClass;
   }
 };
 
 }  // end namespace clang
 
 #endif