DataFormats/TrackerRecHit2D: fix classes_def.xml for multiple definitions

Clean classes_def.xml, not to have multiple definitions for
`sigmaPitch_'

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
Merge pull request #2228 from davidlt/fix-sigmaPitch_-DataFormats/TrackerRecHit2D

ROOT6 -- DataFormats/TrackerRecHit2D: fix classes_def.xml for multiple definitions