ENYO-60: Onyx button elements no longer have a forced line-height.

This corrects an issue regarding onyx applying presumptuous rules to all child button elements, which interferes with other libraries.

Enyo-DCO-1.1-Signed-off-by: Blake Stephens <blake.stephens@lge.com>
Should we update all three for consistency and to avoid the same problem in the future?