#18793: (cli): remove OpenAI tagline from banner

## Summary I just felt like doing it :-) <!-- greptile_comment --> <h3>Greptile Summary</h3> Removes the tagline "OpenAI-compatible, not OpenAI-dependent." from the CLI banner rotation. The change is straightforward and doesn't affect functionality - the banner will simply display one fewer tagline option from the pool of 102+ remaining taglines. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with no risk - Single-line deletion of a string from an array with no logic changes, no syntax changes, and no impact on functionality. The change is cosmetic and the remaining 102+ taglines ensure the feature continues working normally - No files require special attention _{Last reviewed commit: 849f87d} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->