[CMake] don't include eigen.cmake

It is useless

CMakeLists.txt

@@ -55,7 +55,6 @@ IF(NOT EXISTS "${CMAKE_SOURCE_DIR}/cmake/base.cmake")
   MESSAGE(FATAL_ERROR "\nPlease run the following command first:\ngit submodule update --init\n")
 ENDIF()
 
-include(cmake/eigen.cmake)
 include(cmake/boost.cmake)
 include(cmake/python.cmake)
 include(cmake/hpp.cmake)