[cleanups] Remove class CoreCodegen and g_core_codegen_interface (g…

…rpc#31875)

* Delete `g_core_codegen_interface`

* Automated change: Fix sanity tests

* Fix

* Update

BUILD

@@ -242,7 +242,6 @@ GRPCXX_SRCS = [
     "src/cpp/common/channel_arguments.cc",
     "src/cpp/common/channel_filter.cc",
     "src/cpp/common/completion_queue_cc.cc",
-    "src/cpp/common/core_codegen.cc",
     "src/cpp/common/resource_quota_cc.cc",
     "src/cpp/common/rpc_method.cc",
     "src/cpp/common/version_cc.cc",
@@ -264,7 +263,6 @@ GRPCXX_SRCS = [
     "src/cpp/util/byte_buffer_cc.cc",
     "src/cpp/util/string_ref.cc",
     "src/cpp/util/time_cc.cc",
-    "src/cpp/codegen/codegen_init.cc",
 ]
 
 GRPCXX_HDRS = [
@@ -292,7 +290,6 @@ GRPCXX_PUBLIC_HDRS = [
     "include/grpc++/impl/call.h",
     "include/grpc++/impl/channel_argument_option.h",
     "include/grpc++/impl/client_unary_call.h",
-    "include/grpc++/impl/codegen/core_codegen.h",
     "include/grpc++/impl/grpc_library.h",
     "include/grpc++/impl/method_handler_impl.h",
     "include/grpc++/impl/rpc_method.h",
@@ -341,7 +338,6 @@ GRPCXX_PUBLIC_HDRS = [
     "include/grpcpp/impl/channel_argument_option.h",
     "include/grpcpp/impl/channel_interface.h",
     "include/grpcpp/impl/client_unary_call.h",
-    "include/grpcpp/impl/codegen/core_codegen.h",
     "include/grpcpp/impl/completion_queue_tag.h",
     "include/grpcpp/impl/create_auth_context.h",
     "include/grpcpp/impl/delegating_channel.h",
@@ -409,7 +405,6 @@ GRPCXX_PUBLIC_HDRS = [
     "include/grpc++/impl/codegen/completion_queue_tag.h",
     "include/grpc++/impl/codegen/completion_queue.h",
     "include/grpc++/impl/codegen/config.h",
-    "include/grpc++/impl/codegen/core_codegen_interface.h",
     "include/grpc++/impl/codegen/create_auth_context.h",
     "include/grpc++/impl/codegen/metadata_map.h",
     "include/grpc++/impl/codegen/method_handler_impl.h",
@@ -444,7 +439,6 @@ GRPCXX_PUBLIC_HDRS = [
     "include/grpcpp/impl/codegen/completion_queue_tag.h",
     "include/grpcpp/impl/codegen/completion_queue.h",
     "include/grpcpp/impl/codegen/config.h",
-    "include/grpcpp/impl/codegen/core_codegen_interface.h",
     "include/grpcpp/impl/codegen/create_auth_context.h",
     "include/grpcpp/impl/codegen/delegating_channel.h",
     "include/grpcpp/impl/codegen/intercepted_channel.h",