Closes #204

See #204 for details.

This implementation makes #174 and #201 (alternative co2 constraint implementations) unnecessary.

Changes proposed in this Pull Request

Set the co2_emissions of the carrier oil to zero.

[x] I tested my contribution locally and it seems to work fine.
[x] Code and workflow changes are sufficiently documented.
[x] Newly introduced dependencies are added to envs/environment.yaml and envs/environment.docs.yaml.
[x] Changes in configuration options are added in all of config.default.yaml, config.tutorial.yaml, and test/config.test1.yaml.
[x] Changes in configuration options are also documented in doc/configtables/*.csv and line references are adjusted in doc/configuration.rst and doc/tutorial.rst.
[ ] A note for the release notes doc/release_notes.rst is amended in the format of previous release notes, including reference to the requested PR.