chore: drop "oidc_wellknown" tmpl, use json directly (#38731)

`testOAuth2WellKnown` already covers the endpoint's response.

services/context/base.go

@@ -114,7 +114,7 @@ func (b *Base) HTTPError(status int, contents ...string) {
 func (b *Base) JSON(status int, content any) {
 	b.Resp.Header().Set("Content-Type", "application/json;charset=utf-8")
 	b.Resp.WriteHeader(status)
-	if err := json.NewEncoder(b.Resp).Encode(content); err != nil {
+	if err := json.MarshalWrite(b.Resp, content); err != nil {
 		log.Error("Render JSON failed: %v", err)
 	}
 }

services/context/context_response.go

@@ -104,20 +104,6 @@ func (ctx *Context) HTML(status int, name templates.TplName) {
 	}
 }
 
-// JSONTemplate renders the template as JSON response
-// keep in mind that the template is processed in HTML context, so JSON things should be handled carefully, e.g.: use JSEscape
-func (ctx *Context) JSONTemplate(tmpl templates.TplName) {
-	t, err := ctx.Render.TemplateLookup(string(tmpl), nil)
-	if err != nil {
-		ctx.ServerError("unable to find template", err)
-		return
-	}
-	ctx.Resp.Header().Set("Content-Type", "application/json")
-	if err = t.Execute(ctx.Resp, ctx.Data); err != nil {
-		ctx.ServerError("unable to execute template", err)
-	}
-}
-
 // RenderToHTML renders the template content to a HTML string
 func (ctx *Context) RenderToHTML(name templates.TplName, data any) (template.HTML, error) {
 	var buf strings.Builder