William Courtney

Deprecated `gate_set` still set by `CircuitSerializer`

2

The [`CircuitSerializer`](https://github.com/quantumlib/Cirq/blob/f3987d528156f1f746b73fd7b3ca9bdb7e0bd2c3/cirq-google/cirq_google/serialization/circuit_serializer.py#L31) continues to [set](https://github.com/quantumlib/Cirq/blob/f3987d528156f1f746b73fd7b3ca9bdb7e0bd2c3/cirq-google/cirq_google/serialization/circuit_serializer.py#L70) the [deprecated `gate_set`](https://github.com/quantumlib/Cirq/blob/f3987d528156f1f746b73fd7b3ca9bdb7e0bd2c3/cirq-google/cirq_google/api/v2/program.proto#L110) field on `Program` messages. This should be cleaned up, but is blocked by https://github.com/qh-lab/pyle/issues/29210 since the field is actually still required. The...