remove obsolete todo in example

[awaelchli]

What does this PR do?

Removes an obsolete todo about a crashing example, but the example runs fine:

trainer.test(model, datamodule=dm)
and
trainer.test(datamodule=dm)

both work fine after running fit for 1 epoch.
I could not observer any error message described by the todo.

Epoch 0:  92%|█████████▏| 1718/1874 [00:06<00:00, 257.13it/s, loss=0.353, v_num=2]
Validating: 0it [00:00, ?it/s]
Epoch 0:  94%|█████████▍| 1762/1874 [00:06<00:00, 259.86it/s, loss=0.353, v_num=2]
Epoch 0:  96%|█████████▋| 1808/1874 [00:06<00:00, 262.70it/s, loss=0.353, v_num=2]
Validating:  58%|█████▊    | 90/156 [00:00<00:00, 444.70it/s]
Epoch 0: 100%|██████████| 1874/1874 [00:07<00:00, 266.29it/s, loss=0.353, v_num=2]
Epoch 0: 100%|██████████| 1874/1874 [00:07<00:00, 266.10it/s, loss=0.353, v_num=2]
Testing: 100%|██████████| 312/312 [00:00<00:00, 418.23it/s]
--------------------------------------------------------------------------------
DATALOADER:0 TEST RESULTS
{'test_loss': 0.357555627822876}
--------------------------------------------------------------------------------
[{'test_loss': 0.357555627822876}]

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[codecov]

Codecov Report

Merging #6475 (0f2207a) into master (9eded7f) will decrease coverage by 47%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master   #6475     +/-   ##
========================================
- Coverage      94%     47%    -47%     
========================================
  Files         161     161             
  Lines       11497   11835    +338     
========================================
- Hits        10753    5508   -5245     
- Misses        744    6327   +5583