DOC: The use of VersorTransformOptimizerv4 is deprecated.

The use of this optimizer can be replaced by the
RegularStepGradientDescentOptimizerv4 that can generate more precise
results on versor transform optimization.

Change-Id: I987d237f35a2affa5d7b791b34cfeb8d7b37fa7b
Merge topic 'UpdateVersorOptDocs'

96cbca52 DOC: The use of VersorTransformOptimizerv4 is deprecated.