chore: fix some trivial problems and TODOs (#33473)

1. Fix incorrect `MentionCount` (actually it seems to be deadcode,
affects nothing)
2. Remove fallback sha1 support for time limit token
3. Use route middleware `reqRepoActionsWriter` for `ArtifactsDeleteView`
4. Use clearer message "Failed to authenticate user" instead of "Verify"
when auth fails
5. `tests/integration/benchmarks_test.go` is not quite right, actually
it is never used, so delete it.
6. Remove or update TODO comments

models/system/notice_test.go

@@ -45,8 +45,6 @@ func TestCreateRepositoryNotice(t *testing.T) {
 	unittest.AssertExistsAndLoadBean(t, noticeBean)
 }
 
-// TODO TestRemoveAllWithNotice
-
 func TestCountNotices(t *testing.T) {
 	assert.NoError(t, unittest.PrepareTestDatabase())
 	assert.Equal(t, int64(3), system.CountNotices(db.DefaultContext))