Cleanup return_text and return_full_text options in TextGenerationPipeline (#33542)
* Cleanup return_text and return_full_text options in TextGenerationPipeline
* Cleanup return_text and return_full_text options in TextGenerationPipeline
* Cleanup return_text and return_full_text options in TextGenerationPipeline
* Cleanup return_text and return_full_text options in TextGenerationPipeline
* Revert pipeline code, but update docs instead
* Restore pipeline test