Fix broken links (#16113)

* Update marian.mdx

* Update marian.mdx

* Update docs/source/model_doc/marian.mdx
Co-authored-by: Lysandre Debut <lysandre@huggingface.co>

* Update marian.mdx
Co-authored-by: Lysandre Debut <lysandre@huggingface.co>

docs/source/model_doc/marian.mdx

@@ -48,8 +48,7 @@ Translations should be similar, but not identical to output in the test set link
 
 - Since Marian models are smaller than many other translation models available in the library, they can be useful for
   fine-tuning experiments and integration tests.
-- [Fine-tune on GPU](https://github.com/huggingface/transformers/blob/main/examples/research_projects/seq2seq-distillation/train_distil_marian_enro_teacher.sh)
-- [Fine-tune on GPU with pytorch-lightning](https://github.com/huggingface/transformers/blob/main/examples/research_projects/seq2seq-distillation/train_distil_marian_no_teacher.sh)
+- [Fine-tune on GPU](https://github.com/huggingface/transformers/blob/master/examples/legacy/seq2seq/train_distil_marian_enro.sh)
 
 ## Multilingual Models