cv_bridge: numpy test_depend or not?

[racko]

Here python-numpy is listed as a test_depend:

vision_opencv/cv_bridge/package.xml

Line 35 in 9d49971

<test_depend>python-numpy</test_depend>

While here it is required outside of test code:

vision_opencv/cv_bridge/src/CMakeLists.txt

Line 25 in 9d49971

message(SEND_ERROR "Could not determine the NumPy include directory, verify that NumPy was installed correctly.")