fix: remove image in doc

Author: ourai

.knosys/sites/default/src/assets/houston.webp

@@ -4,8 +4,6 @@ description: Get started building your docs site with Starlight.
 template: splash
 hero:
   tagline: Congrats on setting up a new Starlight project!
-  image:
-    file: ../../assets/houston.webp
   actions:
     - text: Contribute
       link: /guides/

.knosys/sites/default/src/content/docs/index.mdx

@@ -4,8 +4,6 @@ description: Get started building your docs site with Starlight.
 template: splash
 hero:
   tagline: Congrats on setting up a new Starlight project!
-  image:
-    file: ../../../assets/houston.webp
   actions:
     - text: 参与共建
       link: /zh/guides/