Remove duplicate SentencePiece package declaration

[yschungmr]

Description:
This PR addresses a redundancy in the requirements.txt file by removing the duplicate declaration of the SentencePiece package. Currently, the package is listed twice:

• As sentencepiece (lowercase, no version specified)
• As SentencePiece==0.1.96 (with specific version)

Changes made:

• Removed the unversioned sentencepiece entry
• Retained SentencePiece==0.1.96 for version consistency

Rationale:

• Python packages are case-insensitive, making these entries effectively duplicate
• Keeping the versioned dependency ensures reproducible builds
• This change maintains project stability while cleaning up the dependency list

Testing:

• Verified that the project builds successfully with the updated requirements.txt
• Confirmed all dependent functionality remains intact

Please review and merge if appropriate.