chore(lua): 删除调度器里两个无人调用的诊断辅助函数

sortedTaskNames / PluginTasks 是开发 Phase 4 时留下的诊断辅助，最终
没有任何调用点（WebUI 走 /api/plugins 的既有结构）。连同不再需要的
sort import 一并删除，保持包面干净。

internal/lua/plugin_runtime.go

@@ -33,7 +33,6 @@ package lua
 
 import (
 	"fmt"
-	"sort"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -638,23 +637,3 @@ func readNumberInt(L *golua.State, idx int, field string) int {
 	}
 	return int(L.ToNumber(-1))
 }
-
-// sortedTaskNames returns the task function names of a spec (for diagnostics).
-func (s scheduleSpec) sortedTaskNames() []string {
-	out := make([]string, 0, len(s.tasks))
-	for _, t := range s.tasks {
-		out = append(out, t.Fn)
-	}
-	sort.Strings(out)
-	return out
-}
-
-// PluginTasks lists the scheduled task names a plugin declared (for diagnostics
-// and for the WebUI to show what periodic work exists).
-func (p *Plugin) PluginTasks() []string {
-	out := make([]string, 0, len(p.Schedule))
-	for _, t := range p.Schedule {
-		out = append(out, t.Fn)
-	}
-	return out
-}