DOC: Fix a bug with SquaredEdgeLengthDecimationQuadEdgeMeshFilter

For an unknown reason, if the first line of the Doxygen comment block
for the SquaredEdgeLengthDecimationQuadEdgeMeshFilter::MeasureEdge and
::Relocate functions is blank, Doxygen fails in several significant ways.
This change fixes the content of the documentation and prevents warnings.

Change-Id: Ic66e494a411fc2bb3daa7acbb46d80d9cc56b2a6
Merge topic 'Doxygen-Warning'

7a238de DOC: Fix a bug with SquaredEdgeLengthDecimationQuadEdgeMeshFilter