Convert legacy auth server to non-builtin plugin on posix

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@58728 65644016-39b1-43b1-bf79-96bc8fe82c15
Cleanup - we anyway do not support protocol to talk to ancient servers

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@58729 65644016-39b1-43b1-bf79-96bc8fe82c15
Rollback some of my wrong changes

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@58730 65644016-39b1-43b1-bf79-96bc8fe82c15