CMake: Remove tealeaf reader mode

*** This removes support for CMake < 3.7 ***

Change-Id: Iddb0bab1a61b814adb4cb7ffa217284e96cb1140
Reviewed-by: Cristian Adam <cristian.adam@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/cmakeprojectmanager/builddirreader.cpp

@@ -27,7 +27,6 @@
 
 #include "fileapireader.h"
 #include "servermodereader.h"
-#include "tealeafreader.h"
 
 #include <utils/qtcassert.h>
 
@@ -51,7 +50,7 @@ std::unique_ptr<BuildDirReader> BuildDirReader::createReader(const BuildDirParam
     case CMakeTool::ServerMode:
         return std::make_unique<ServerModeReader>();
     default:
-        return std::make_unique<TeaLeafReader>();
+        return {};
     }
 }