[MM-16791] Migrate Plugin.Delete to Sync by default (#11580)

* Migrate Plugin.Delete to Sync by default

* remove unused import

store/storetest/mocks/PluginStore.go

@@ -6,7 +6,6 @@ package mocks
 
 import mock "github.com/stretchr/testify/mock"
 import model "github.com/mattermost/mattermost-server/model"
-import store "github.com/mattermost/mattermost-server/store"
 
 // PluginStore is an autogenerated mock type for the PluginStore type
 type PluginStore struct {
@@ -37,15 +36,15 @@ func (_m *PluginStore) CompareAndSet(keyVal *model.PluginKeyValue, oldValue []by
 }
 
 // Delete provides a mock function with given fields: pluginId, key
-func (_m *PluginStore) Delete(pluginId string, key string) store.StoreChannel {
+func (_m *PluginStore) Delete(pluginId string, key string) *model.AppError {
 	ret := _m.Called(pluginId, key)
 
-	var r0 store.StoreChannel
-	if rf, ok := ret.Get(0).(func(string, string) store.StoreChannel); ok {
+	var r0 *model.AppError
+	if rf, ok := ret.Get(0).(func(string, string) *model.AppError); ok {
 		r0 = rf(pluginId, key)
 	} else {
 		if ret.Get(0) != nil {
-			r0 = ret.Get(0).(store.StoreChannel)
+			r0 = ret.Get(0).(*model.AppError)
 		}
 	}