Remove git merge markers from docs/content/mongocxx-v3/client-side-encryption.md

https://github.com/mongodb/mongo-cxx-driver/blob/915586cb5a87524b1f1dc3944b38becd53391013/docs/content/mongocxx-v3/client-side-encryption.md#L86-L87

has git merge markers in the file (i.e. <<<<<< HEAD). These should be removed to improve readability of the documentation.