Remove or update qasm2 examples

[jon-wurtz]

Most of our examples use the outdated qasm2 dialect set, eg https://bloqade.quera.com/latest/digital/examples/qasm2/qft/. This dialect set is outdated and superseded by squin.

1. Remove these examples to avoid confusion with new users
2. Update the examples to work in squin instead of qasm2

[david-pl]

Just to clarify: this should be replace all qasm2.extended examples. The basic qasm2.main dialect is still fine and won't be removed. I'll have to check though whether we are even using that in any examples.