Remove bazel

[balopat]

Description of the issue

Now that there is no dependency of TFQ on our protos (tensorflow/quantum#590), we can remove all the bazel functionality.

[95-martin-orion]

How does this interact with Google-internal usage of Cirq, which is (or will soon be) required for QCS? Presumably, the internal code relies on internal Bazel for building Cirq - we should make sure that those definitions are preserved (even if they move to internal-only).

We can discuss the internal Cirq requirements offline if you have questions.

[balopat]

My understanding is that it does not interact with it at all. The BUILD/WORKSPACE files are all excluded in the copybara imports and have instead alternative versions controlled internally for blaze (otherwise internal targets would need to be open sourced, which would not be too meaningful).