Consider dropping or simplifying `ConnectionImpl::*_policy()` getters

[dbolduc]

We do not need the else branch that uses the connection's options_ in this code: https://github.com/googleapis/google-cloud-cpp/blob/292265193edcbe6737cde4053145610a5f3e267d/google/cloud/tpu/internal/tpu_connection_impl.h#L89-L119

These policy options are defaulted in the connection, and passed back to the client. This means that any OptionsSpan the client creates will have the policy options we should use present.

We may need to update some unit tests for the ConnectionImpls which do not have a client present to create such a span.

[devbww]

We may need to update some unit tests for the ConnectionImpls which do not have a client present to create such a span.

For the record, here is the comment that describes the current behavior of those tests.

https://github.com/googleapis/google-cloud-cpp/blob/292265193edcbe6737cde4053145610a5f3e267d/generator/internal/connection_impl_generator.cc#L113-L117

[coryan]

@dbolduc thinks there is not enough value. Closing.

[coryan]

This is now fixed.