Revert "Support conversion of #unstub"

This reverts commit 1daa0216fe07810f3bd4f1e4158927aa33609bb5.

Currently `allow(obj).to receive(:message).and_call_original` does not
work as well as `unstub` sometimes.

https://github.com/rspec/rspec-mocks/issues/613
Bump up version to 1.10.0