remove plugin version for automigrate as it was used only in v24 and v28 that have been removed

apps/dashboard/pkg/migration/schemaversion/migrations.go

@@ -9,9 +9,6 @@ import (
 const (
 	MIN_VERSION    = 12
 	LATEST_VERSION = 42
-
-	// The pluginVersion to set after simulating auto-migrate for angular panels
-	pluginVersionForAutoMigrate = "12.1.0"
 )
 
 type SchemaVersionMigrationFunc func(context.Context, map[string]interface{}) error