Fixed the succes rate metrics on the Prompting Guide (#37)

Co-authored-by: Valentin Foucault <valentin@vapi.ai>

Author: valentin-fclt

fern/prompting-guide.mdx

@@ -17,8 +17,6 @@ Prompt engineering is crucial when building AI Agents because it determines how
 
 In the context of Voice AI Agents, we consider your "success rate" to be the percentage of requests your Agent manages to successfully handle from start to finish, without the intervention of a human.
 
-Depending on your use case and how much you iterate on your prompt, we find that our users typically achieve a **60-95%** success rate. A success rate of more than **90%** can usually be considered satisfactory.\
-\
 The more complex your use case is, the more you will have to make experiments and iterate on your prompt to improve your success rate.
 
 ## The process