Disable building of zlibstream.cxx for now

It is unclear to me how to correctly fix some of the remaining build
errors obtained on jenkins, therefore I am disabling it from the build
for now.

simgear/io/iostreams/CMakeLists.txt

@@ -4,14 +4,12 @@ set(HEADERS
     sgstream.hxx
     gzfstream.hxx
     gzcontainerfile.hxx
-    zlibstream.hxx
     )
 
 set(SOURCES
     sgstream.cxx
     gzfstream.cxx
     gzcontainerfile.cxx
-    zlibstream.cxx
     )
 
 simgear_component(IOStreams io/iostreams "${SOURCES}" "${HEADERS}")
@@ -22,8 +20,4 @@ if(ENABLE_TESTS)
   target_link_libraries(test_streams ${TEST_LIBS})
   add_test(streams ${EXECUTABLE_OUTPUT_PATH}/test_streams)
 
-  add_executable(test_zlibstream zlibstream_test.cxx)
-  target_link_libraries(test_zlibstream ${TEST_LIBS})
-  add_test(zlibstream ${EXECUTABLE_OUTPUT_PATH}/test_zlibstream)
-
 endif(ENABLE_TESTS)