Remove remaining thrift-based code from main repo

Deprecated-on-arrival: Re-enable public constructor for ClientAsyncResponseReader 

Add support for Trailers-Only responses.

- When receiving a Trailers-Only response, return the metadata as
  trailing metadata instead of initial metadata.
- Send Trailers-Only response when we have no non-default initial metadata,
  no message to send, and trailing metadata to send.

Re-enable public constructor for ClientAsyncResponseReader to avoid busting client that bypassed code generator. This code is deprecated-on-arrival as it is a performance pessimization. This code path should not be used.

Remove long long

Still create channel if remotedb is false. Just do not use it in the …

Tracing Overhaul

Fix ObjC memory leak problem

Fix license file

Grammar fix in issue template

Regenerate Projects, Sanity

QPS Driver Diff

Batch push_setting

Upgrade boringssl

Fix max_message_length

Unref existing error before setting a new one.

Remove lockfree-stack implementation that is no longer used

Eliminate some allocations in client_channel code.