COMP: Remove incorrect override declaration

This patch addresses the following compilation error:
'void itk::GradientDescentOptimizerv4Template<TInternalComputationValueType>::AdvanceOneStep()
[with TInternalComputationValueType = double]' marked override, but
does not overridve

Change-Id: I56e470d25356f8c3cd2faa7ac737cbc1071d1ba0
Merge topic 'FixNonOverrideAdvanceOneStep'

6393e041 COMP: Remove incorrect override declaration