[Docs]Fix documentation formatting in architecture overview (#34679)

Signed-off-by: codedump <lichuang1982@gmail.com>
Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>
Co-authored-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

docs/design/arch_overview.md

@@ -208,9 +208,7 @@ configurations affect the class we ultimately get.
 
 The following figure shows the class hierarchy of vLLM:
 
-> <figure markdown="span">
->   ![](../assets/design/hierarchy.png){ align="center" alt="query" width="100%" }
-> </figure>
+![Class Hierarchy](../assets/design/hierarchy.png)
 
 There are several important design choices behind this class hierarchy: