Get rid of `with` statement

[delphidabbler]

There's a with statement in function beginning at line 504 of PJMD5.pas:

md5/PJMD5.pas

Line 504 in 1e6aac0

class function TPJMD5.Calculate(const Buf; const Count: Cardinal): TPJMD5Digest;

Refactor it out.