cleanup(storage): remove deprecated OpenTelemetry rpc.message.type and rpc.message.id attributes #16544

Summary

Several async Cloud Storage tracing implementations currently record span events with the hardcoded string literals /*sc::kRpcMessageType=*/"rpc.message.type" and /*sc::kRpcMessageId=*/"rpc.message.id".

In OpenTelemetry Semantic Conventions v1.40.0 (introduced in opentelemetry-cpp v1.26.0 in <opentelemetry/semconv/incubating/rpc_attributes.h>), opentelemetry::semconv::rpc::kRpcMessageType and opentelemetry::semconv::rpc::kRpcMessageId were marked OPENTELEMETRY_DEPRECATED with:

• "reason": "obsoleted"
• "note": "Deprecated, no replacement at this time."

Because these semantic convention attributes are obsolete upstream with no replacement, we should remove or clean up our usage of "rpc.message.type" and "rpc.message.id" in google/cloud/storage/internal/async/.

Background

• These attributes were originally added/updated as string literals in:
  • chore(otel): use newer messaging semantic conventions #14373 (chore(otel): use newer messaging semantic conventions)
  • feat(storage): Add bidiread and bidi appendable write to the async client. #15078 (feat(storage): Add bidiread and bidi appendable write to the async client.)
  • fix(storage): Add telemetry tracing support for async stream Close() #16118 (fix(storage): Add telemetry tracing support for async stream Close())
• Unlike other /*sc::...=*/ string literals across the codebase, we intentionally did not migrate these to opentelemetry::semconv::rpc::kRpcMessageType / kRpcMessageId because doing so triggers -Wdeprecated-declarations compiler warnings when building against opentelemetry-cpp >= 1.26.0.

Affected Files

• google/cloud/storage/internal/async/object_descriptor_reader_tracing.cc
• google/cloud/storage/internal/async/reader_connection_tracing.cc
• google/cloud/storage/internal/async/reader_connection_tracing_test.cc
• google/cloud/storage/internal/async/writer_connection_tracing.cc
• google/cloud/storage/internal/async/writer_connection_tracing_test.cc