[hotfix] Remove fx training flag in entry point

[illian01]

Description

Please include a summary in English, of the changes in this pull request. If it closes an issue, please mention it here.

Closes: #187

You should link at least one existing issue for PR. Before your create a PR, please check to see if there is an issue for this change.
PRs from forked repository not accepted.

Change(s)

• Remove fx training flag in src/netspresso_trainer/train.py

Changelog

If you PR to dev branch, please add a brief summary of the change to the Upcoming Release section of the CHANGELOG.md file and include a link to the PR (formatted in markdown) and a link to your github profile.

For example,

- Added a new feature by `@myusername` in [PR 2023](https://github.com/Nota-NetsPresso/netspresso-trainer/pull/2023)

Code Formatting

If you PR to either master or dev branch, you should follow the code linting process. Please check your code with lint_check.sh in ./scripts directory.
For more information, please read the contribution guide in CONTRIBUTING.md.

[deepkyu]

Thx for your proactive work