Uncomment and fix `Thresholding` module tests

### Description

Fix and uncomment the `itkIntermodesThresholdImageFilterTestNoAutoMinMax` and `itkOtsuThresholdCalculatorVersusOtsuMultipleThresholdsCalculatorTest` [tests](https://github.com/InsightSoftwareConsortium/ITK/blob/master/Modules/Filtering/Thresholding/test/CMakeLists.txt) in the `Thresholding` module. They were commented to so that the related PR could be moved forward and be merged.

### Steps to Reproduce

1. Uncomment `itkIntermodesThresholdImageFilterTestNoAutoMinMax` and `itkOtsuThresholdCalculatorVersusOtsuMultipleThresholdsCalculatorTest` tests.
2. Configure and build ITK.
3. Run the tests, e.g.
```
ctest -V -R itkIntermodesThresholdImageFilterTestNoAutoMinMax -C Debug
```
and
```
ctest -V -R itkOtsuThresholdCalculatorVersusOtsuMultipleThresholdsCalculatorTest -C Debug
```
from the binaries directory.

### Expected behavior

Both tests should pass and yield the expected results.

### Actual behavior

None of the two tests pass:
- `itkIntermodesThresholdImageFilterTestNoAutoMinMax` exceeds the allowed number maximum number of smoothing iterations, whatever its value is.
- `itkOtsuThresholdCalculatorVersusOtsuMultipleThresholdsCalculatorTest` fails when comparing the values of the values yielded by `itk::OtsuThresholdsCalculator` and the `itk::OtsuMultipleThresholdsCalculator` instances.

### Reproducibility

%100.

### Versions

`master`.

### Environment

All environments.

### Additional Information

See [this comment](https://github.com/InsightSoftwareConsortium/ITK/pull/511#issuecomment-605536928) and the context in PR #511.

@richardbeare may be you have some intuition of what the cause may be.