Quantum Chess: Update concept docs to recirq

[dstrain115]

The quantum chess concept docs still refer to large code blocks that are now in recirq. These should mostly (or completely) moved to the relevant pointers in recirq.

For instance, in the dynamic qubit mapping:
https://quantumai.google/cirq/experiments/quantum_chess/concepts#dynamic_qubit_mapping
Can point to this source code instead:
https://github.com/quantumlib/ReCirq/blob/master/recirq/quantum_chess/circuit_transformer.py#L25

This pattern is repeated throughout the document.

Quantum concepts doc display:
https://quantumai.google/cirq/experiments/quantum_chess/concepts#quantum_chess_in_cirq

Document source:
https://github.com/quantumlib/ReCirq/blob/master/docs/quantum_chess/concepts.ipynb