Remove unnecessary meta data on markdown files (#12)

Reviewed-on: https://gitea.com/gitea/docs/pulls/12

docs/contributing/guidelines-backend.md

@@ -3,16 +3,8 @@ date: "2021-11-01T23:41:00+08:00"
 title: "Guidelines for Backend Development"
 slug: "guidelines-backend"
 sidebar_position: 20
-toc: false
-draft: false
 aliases:
   - /en-us/guidelines-backend
-menu:
-  sidebar:
-    parent: "contributing"
-    name: "Guidelines for Backend"
-    sidebar_position: 20
-    identifier: "guidelines-backend"
 ---
 
 # Guidelines for Backend Development

docs/contributing/guidelines-frontend.md

@@ -3,16 +3,8 @@ date: "2021-10-13T16:00:00+02:00"
 title: "Guidelines for Frontend Development"
 slug: "guidelines-frontend"
 sidebar_position: 30
-toc: false
-draft: false
 aliases:
   - /en-us/guidelines-frontend
-menu:
-  sidebar:
-    parent: "contributing"
-    name: "Guidelines for Frontend"
-    sidebar_position: 30
-    identifier: "guidelines-frontend"
 ---
 
 # Guidelines for Frontend Development

docs/contributing/guidelines-refactoring.md

@@ -3,16 +3,8 @@ date: "2023-02-14T00:00:00+00:00"
 title: "Guidelines for Refactoring"
 slug: "guidelines-refactoring"
 sidebar_position: 40
-toc: false
-draft: false
 aliases:
   - /en-us/guidelines-refactoring
-menu:
-  sidebar:
-    parent: "contributing"
-    name: "Guidelines for Refactoring"
-    sidebar_position: 40
-    identifier: "guidelines-refactoring"
 ---
 
 # Guidelines for Refactoring

docs/contributing/localization.md

@@ -3,16 +3,8 @@ date: "2016-12-01T16:00:00+02:00"
 title: "Localization"
 slug: "localization"
 sidebar_position: 70
-toc: false
-draft: false
 aliases:
   - /en-us/localization
-menu:
-  sidebar:
-    parent: "contributing"
-    name: "Localization"
-    sidebar_position: 70
-    identifier: "localization"
 ---
 
 # Localization