Revert previous two commits

Revert previous two commits

It turns out we still support pre-auth compression on the client.
Therefore revert the previous two commits:

date: 2018/07/06 09:06:14;  author: sf;  commitid: yZVYKIRtUZWD9CmE;
  Rename COMP_DELAYED to COMP_ZLIB

  Only delayed compression is supported nowadays.

  ok markus@

date: 2018/07/06 09:05:01;  author: sf;  commitid: rEGuT5UgI9f6kddP;
  Remove leftovers from pre-authentication compression

  Support for this has been removed in 2016.
  COMP_DELAYED will be renamed in a later commit.

  ok markus@