[cmake] clean findnumpy

[gouzil]

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Description

清除在FindNumPy.cmake指定cmake最小版本

具体警告如下

CMake Deprecation Warning at cmake/FindNumPy.cmake:6 (cmake_minimum_required):
  Compatibility with CMake < 2.8.12 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.
Call Stack (most recent call first):
  cmake/external/python.cmake:76 (find_package)
  cmake/third_party.cmake:376 (include)
  CMakeLists.txt:601 (include)

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