Remove how_to_train.md: outdated training FAQ (#4267)

Co-authored-by: behroozazarkhalili <ermiaazarkhalili>

Author: behroozazarkhalili

docs/source/_toctree.yml

@@ -13,8 +13,6 @@
     title: Paper Index
   - local: experimental
     title: Experimental
-  - local: how_to_train
-    title: Training FAQ
   title: Conceptual Guides
 - sections:
   - local: clis

docs/source/how_to_train.md

@@ -91,7 +91,6 @@ trl reward --model_name_or_path Qwen/Qwen2.5-0.5B-Instruct \
 - [SFT Trainer](sft_trainer) - Complete SFT guide
 - [DPO Trainer](dpo_trainer) - Preference alignment
 - [GRPO Trainer](grpo_trainer) - Group relative policy optimization
-- [Training FAQ](how_to_train) - Common questions
 
 ### 🚀 Scale Up
 
@@ -141,4 +140,4 @@ Try adjusting the learning rate:
 training_args = SFTConfig(learning_rate=2e-5)  # Good starting point
 ```
 
-For more help, see our [Training FAQ](how_to_train) or open an [issue on GitHub](https://github.com/huggingface/trl/issues).
+For more help, open an [issue on GitHub](https://github.com/huggingface/trl/issues).