Update FilUtil#backup, #removeOldBackup and its caller

[miurahr]

Refactoring FileUtil#removeOldBackups and Update RealProject#loadTranslations to check backup file creation and record it as log message.

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Please check the type of change your PR introduces:

• [ ] Bug fix
• [ ] Feature
• [ ] Documentation
• [ ] Build and release changes
• [x] Other (describe below)

Improve safety and visibility of backup file creation

Which ticket is resolved?

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What does this PR change?

• use lambda in removeOldBackup method to improve code clearer
• check return value from backup method and record it in log

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