Remove stale and potentially unused code Request.writeEncryptedScalarStream

The code in net.Request.writeEncryptedScalarStream() is in a bad state, for instance:

• it materializes the stream
• it doesn't support streams longer than Integer.MAX_VALUE
  (this is fine for BLOB since Derby limits the LOB size to 2G-1, but for CLOBs the data stream may be longer since the length is expressed in characters)
• in some error situations it causes a disconnect

Since the security mechanisms required to run this code (SECMEC_EUSRIDDTA and SECMEC_EUSRPWDDTA) are apparently supported in the client but not in the network server, deleting it seems like a good option considering its state.