[Bugfix] Added rm -f / wget- nc command in multispeaker sim notebook pushing to r1.13.0
Signed-off-by: Taejin Park <tango4j@gmail.com>

# What does this PR do ?

Fix minor bugs in multispeaker simulation tutorial notebook
https://github.com/NVIDIA/NeMo/blob/main/tutorials/tools/Multispeaker_Simulator.ipynb

Bugfix for 
https://nvbugswb.nvidia.com/NvBugs5/SWBug.aspx?bugid=3848353

- rm throws out an error if there is no such file

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

# Changelog 


added rm -f (try deleting only if file exists)
added wget -nc  (no duplication)


# Usage

Please run the tutorial notebook

# 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?

any one in ASR

# Additional Information
* Related to # (issue)
