Remove unused DigestString and DigestStream from TBoldMD5

[bero]

Summary

Removed two unused class methods from TBoldMD5:

• DigestString - computed MD5 hash from a string
• DigestStream - computed MD5 hash from a stream

Changes

• File: Source/BoldMD5.pas
• Removed Classes unit from uses clause (no longer needed)
• Removed 46 lines of unused code

Rationale

These methods were not referenced anywhere in the codebase and added unnecessary code surface area.