Rendering aborted due to complexity issues. If this is valid markdown, please feel free to open an issue and attach the original markdown to the issue.

This reverts commit 79759fea, reversing
changes made to dc36f4df.

php ```is_a``` function expects fully qualified class name to validate.

Requires synchronous and single-threaded, so only 1 channel and 1 outstanding RPC
per channel for now. No open-loop for now

completion_queue_next() loop in grpc_php_shutdown_completion_queue
function as it is no longer needed. This was most likely an artifact of
a previous version of grpc-core where completion queues did not have a
"one tag in, one tag out" rule