[clangd] NFC: Use deprecated grpc++ headers for compatibility

Summary:
Ubuntu 18.04 and older versions do not provide latest gRCP packages and the
ones that are in the repository use deprecated headers. Use these headers to
make builds possible.

https://packages.ubuntu.com/bionic/amd64/libgrpc++-dev/filelist

Reviewers: sammccall

Reviewed By: sammccall

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, kadircet, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D79487

clang-tools-extra/clangd/index/remote/Client.cpp

@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include <grpcpp/grpcpp.h>
+#include <grpc++/grpc++.h>
 
 #include "Client.h"
 #include "Index.grpc.pb.h"

clang-tools-extra/clangd/index/remote/server/Server.cpp

@@ -13,8 +13,8 @@
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Signals.h"
 
-#include <grpcpp/grpcpp.h>
-#include <grpcpp/health_check_service_interface.h>
+#include <grpc++/grpc++.h>
+#include <grpc++/health_check_service_interface.h>
 
 #include "Index.grpc.pb.h"