ENH: Always enable Get*FromTag methods in GDCMImageIO

The GetValueFromTag and GetLabelFromTag methods don't require a
static buffer and should be fully compatible with GDCM 2.

Both function provide a major convenience and should not be
depreciated.

The functions were deprecated by
f00506be172c9d89314695788770e264f782a6d3

Change-Id: Ide5ef2b873452473dc22bafa6986ffb821a00466
Merge topic 'gdcm-tag'

1eab6cb ENH: Always enable Get*FromTag methods in GDCMImageIO