remove examples and instances

theories/examples/counterexamples.v

theories/examples/keyideas/generalized_simulations.v

theories/examples/keyideas/simulations.v

theories/examples/refinements/derived.v

theories/examples/refinements/memoization.v

theories/examples/refinements/refinement.v

theories/examples/safety/assert.v

theories/examples/safety/barrier/barrier.v

theories/examples/safety/barrier/example_client.v

theories/examples/safety/barrier/proof.v

theories/examples/safety/barrier/specification.v

theories/examples/safety/clairvoyant_coin.v

theories/examples/safety/counter.v

theories/examples/safety/lazy_coin.v

theories/examples/safety/lock.v

theories/examples/safety/nondet_bool.v

theories/examples/safety/par.v

theories/examples/safety/spawn.v

theories/examples/safety/spin_lock.v

theories/examples/safety/ticket_lock.v