chore: cleanup deprecated extension yaml (#6245)

#### What type of PR is this?
/kind cleanup
/area core
/milestone 2.17.x

#### What this PR does / why we need it:
清理已经过时很久的 yaml extension 声明

#### Does this PR introduce a user-facing change?
```release-note
None
```

application/src/main/java/run/halo/app/search/PostDocUtils.java

@@ -1,20 +0,0 @@
-package run.halo.app.search;
-
-import run.halo.app.search.post.PostDoc;
-import run.halo.app.theme.finders.vo.PostVo;
-
-public enum PostDocUtils {
-    ;
-
-    // TODO Move this static method to other place.
-    public static PostDoc from(PostVo postVo) {
-        return new PostDoc(
-            postVo.getMetadata().getName(),
-            postVo.getSpec().getTitle(),
-            postVo.getStatus().getExcerpt(),
-            postVo.getContent().getContent(),
-            postVo.getSpec().getPublishTime(),
-            postVo.getStatus().getPermalink()
-        );
-    }
-}

application/src/main/resources/extensions/extension-definitions.yaml

@@ -1,20 +1,6 @@
 ## TODO: Currently, Halo does not support i18n for configuration file descriptions
 ## So Simplified Chinese is temporarily used as the default description language.
 
-# TODO Remove the username-password-authenticator in the future.
-apiVersion: plugin.halo.run/v1alpha1
-kind: ExtensionDefinition
-metadata:
-  name: username-password-authenticator
-  labels:
-    auth.halo.run/extension-point-name: "additional-webfilter"
-  deletionTimestamp: 2024-02-18T08:27:41.257531Z
-spec:
-  className: run.halo.app.security.authentication.login.UsernamePasswordAuthenticator
-  extensionPointName: additional-webfilter
-  displayName: "UsernamePasswordAuthenticator"
-  description: "Authenticates a user by username and password."
----
 apiVersion: plugin.halo.run/v1alpha1
 kind: ExtensionDefinition
 metadata:

application/src/main/resources/extensions/role-template-uc-content.yaml

@@ -11,23 +11,6 @@ metadata:
       ["role-template-manage-posts"]
 rules: [ ]
 
----
-apiVersion: v1alpha1
-kind: "Role"
-metadata:
-  name: role-template-post-editor
-  # Deprecated, will be removed in the future
-  deletionTimestamp: 2023-12-01T03:36:25.875373Z
-  labels:
-    halo.run/role-template: "true"
-  annotations:
-    rbac.authorization.halo.run/module: "Posts Management"
-    # Currently, yaml definition does not support i18n, please see https://github.com/halo-dev/halo/issues/3573
-    rbac.authorization.halo.run/display-name: "Post Editor"
-    rbac.authorization.halo.run/dependencies: |
-      ["role-template-manage-posts", "role-template-post-author"]
-rules: [ ]
-
 ---
 apiVersion: v1alpha1
 kind: "Role"