COMP: Remove unused TransformFileWriter::m_Precision ivar

Resolves issue 3183:

https://issues.itk.org/jira/browse/ITK-3183

Change-Id: Idefce0cb502d47c479d22969bc182d8ce38db569
Merge topic 'remove-dead-TransformFileWriter-m_Precision'

a05095d COMP: Remove unused TransformFileWriter::m_Precision ivar