After commit 64080e632, configure checks for all the header files that
should be available in OpenCV 2.3 and later. If any of these files isn't
there the OpenCV elements won't be part of the build.
No need to recheck for opencv2/legacy/legacy.hpp again in
gstpyramidsegment.h. Minimum supported OpenCV version must have this header
and configure already checks for it. Removing check.