Remove circular imports
Signed-off-by: Taejin Park <tango4j@gmail.com>

# What does this PR do ?

This PR fixes the bug in https://nvbugswb.nvidia.com/NvBugs5/SWBug.aspx?bugid=3839247
A couple of functions from `speaker_utils.py` was causing a circular import error.
The function calls are removed and tested training/inference based on `DiarizationSpeechLabel` class.

**Collection**: [Note which collection this PR will affect]
ASR

# Changelog 

Removed function imports from `speaker_utils.py` to solve circular import error.

# Usage
* You can potentially add a usage example below

```python

python ./multiscale_diar_decoder.py --config-path='../conf/neural_diarizer' --config-name='msdd_5scl_15_05_50Povl_256x3x32x2.yaml' \
    trainer.devices=1 \
    model.base.diarizer.speaker_embeddings.model_path="titanet_large" \
    model.train_ds.manifest_filepath="<train_manifest_path>" \
    model.validation_ds.manifest_filepath="<dev_manifest_path>" \
    model.train_ds.emb_dir="<train_temp_dir>" \
    model.validation_ds.emb_dir="<dev_temp_dir>" \
    exp_manager.name='sample_train' \
    exp_manager.exp_dir='./msdd_exp'
```

# Before your PR is "Ready for review"
**Pre checks**:
- [x] Make sure you read and followed [Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md)
- [x] Did you write any new necessary tests?
- [x] Did you add or update any necessary documentation?
- [ ] Does the PR affect components that are optional to install? (Ex: Numba, Pynini, Apex etc)
  - [ ] Reviewer: Does the PR have correct import guards for all optional libraries?
  
**PR Type**:
- [ ] New Feature
- [x] Bugfix
- [ ] Documentation

If you haven't finished some of the above items you can still open "Draft" PR.


## Who can review?

Anyone in the community is free to review the PR once the checks have passed. 
[Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md) contains specific people who can review PRs to various areas.

# Additional Information
* Related to https://nvbugswb.nvidia.com/NvBugs5/SWBug.aspx?bugid=3839247