cmSystemTools: remove `ComputeStringMD5` method

No longer used.

Source/cmSystemTools.cxx

@@ -1316,12 +1316,6 @@ std::string cmSystemTools::ComputeFileHash(const std::string& source,
   return hash.HashFile(source);
 }
 
-std::string cmSystemTools::ComputeStringMD5(const std::string& input)
-{
-  cmCryptoHash md5(cmCryptoHash::AlgoMD5);
-  return md5.HashString(input);
-}
-
 #  ifdef _WIN32
 std::string cmSystemTools::ComputeCertificateThumbprint(
   const std::string& source)

Source/cmSystemTools.h

@@ -219,9 +219,6 @@ public:
   static std::string ComputeFileHash(const std::string& source,
                                      cmCryptoHash::Algo algo);
 
-  /** Compute the md5sum of a string.  */
-  static std::string ComputeStringMD5(const std::string& input);
-
 #  ifdef _WIN32
   //! Get the SHA thumbprint for a certificate file
   static std::string ComputeCertificateThumbprint(const std::string& source);