Revert use of protobuf's Gzip streams.

Unfortunately some Red Hat-based distributions lack the required header.
See https://bugzilla.redhat.com/show_bug.cgi?id=815587

This reverts commit 261a389a76.
This reverts commit b6736eb0a5.

configure.ac

@@ -155,6 +155,8 @@ AS_IF([test x"$with_utempter" != xno],
       [AC_MSG_WARN([Unable to find libutempter; utmp entries will not be made.])],
       [AC_MSG_ERROR([--with-utempter was given but libutempter was not found.])])])])
 
+AC_SEARCH_LIBS([compress], [z], , [AC_MSG_ERROR([Unable to find zlib.])])
+
 AC_ARG_WITH([skalibs],
   [AS_HELP_STRING([--with-skalibs[=DIR]],
      [root directory of skalibs installation])],