build: Fix some unused variable warnings

[tbarrella]

Commit Message: build: Fix some unused variable warnings
Additional Description:
Risk Level: Low
Testing: bazel build
Docs Changes: N/A
Release Notes: N/A
Platform Specific Features:

[antoniovicente]

Thanks for the cleanup!

[lambdai]

I saw _ is used else where. e.g.

    auto [_, inserted] = timer_map.insert(std::make_pair(timer_type, minimum));

Since you didn't fix the _ it means _ could be massage the compiler and avoid the UNREFERENCED_PARAMETER

[antoniovicente]

I saw _ is used else where. e.g.

    auto [_, inserted] = timer_map.insert(std::make_pair(timer_type, minimum));

Since you didn't fix the _ it means _ could be massage the compiler and avoid the UNREFERENCED_PARAMETER

_ is not special in C++. There's examples of UNREFERENCED_PARAMETER(_); in the envoy codebase, for example:

https://github.com/envoyproxy/envoy/blob/master/test/server/filter_chain_benchmark_test.cc#L250

[tbarrella]

Yeah, the compiler complained about _ too.. this only does some warnings; I'd given up

[lambdai]

I saw _ is used else where. e.g.

    auto [_, inserted] = timer_map.insert(std::make_pair(timer_type, minimum));

Since you didn't fix the _ it means _ could be massage the compiler and avoid the UNREFERENCED_PARAMETER

_ is not special in C++. There's examples of UNREFERENCED_PARAMETER(_); in the envoy codebase, for example:

https://github.com/envoyproxy/envoy/blob/master/test/server/filter_chain_benchmark_test.cc#L250

Interesting. That line is added by me...

Then renaming to "_" doesn't make much sense.

I am not sure which compiler is complaining but this PR is good