DOC: Made AnisotropicDiffusion documentation consistent with code

The documentation for both itkAnisotropicDiffusionFunction.h and
itkAnisotropicDiffusionImageFilter.h listed incorrect guidance for how
to set the m_TimeStep parameter compared with the code.
The documentation is now consistent between the two files and the
code.

Change-Id: I77b7ddc2c8909c36dbddd5b70a63b7a2aa8a2f10
BUG: Inconsistency detected by ld.so due to static const string

Change-Id: I77f98557c0e905247fedde14243c25fc9d731b8f
Merge topic 'otb-ITK-3012-lderror'

3343643 BUG: Inconsistency detected by ld.so due to static const string
Merge topic 'AnisotropicDiffusionDocumentation'

c05b73c DOC: Made AnisotropicDiffusion documentation consistent with code