refactor(cat-voices): 1128 remove openapi

[LynxLynxx]

Description

Remove OpenAPI spec flutter code generation

Related Issue(s)

Resolves #1128

Description of Changes

• Remove code-generator and test-flutter-code-generator targets from catalyst_voices/Earthfile.
• Remove dependencies pulled by code-generator and test-flutter-code-generator which are no longer needed (chopper, etc)
• Remove generated cat_cateway_api files
• Remove references to code-generator and test-flutter-code-generator across the project (Justfile, README, etc).

Related Pull Requests

Relates to input-output-hk/catalyst-ci#350

Please confirm the following checks

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream module

[github-actions]

✅ Test Report | ${\color{lightgreen}Pass: 320/320}$ | ${\color{red}Fail: 0/320}$ |

[stevenj]

LGTM

[github-actions]

✅ Test Report | ${\color{lightgreen}Pass: 320/320}$ | ${\color{red}Fail: 0/320}$ |

[github-actions]

✅ Test Report | ${\color{lightgreen}Pass: 320/320}$ | ${\color{red}Fail: 0/320}$ |

[github-actions]

✅ Test Report | ${\color{lightgreen}Pass: 320/320}$ | ${\color{red}Fail: 0/320}$ |