Removed year component from version field.

Removed the name of the edition of the DICOM standard, i.e. "2014a" for the
current edition, from the version field of each DICOM attribute. Since the
DICOM standard will now be published/updated more often, the complete data
dictionary will be generated automatically several times a year. Having the
year component in the version field would change each entry every time and
would make it hard (if not impossible) to see what has actually changed.