Charts Axis - hideFirstMajorUnit/hideLastMajorUnit bug fix.

Address issue in which start/end axis points/labels were being incorrectly deleted from their respective attributes when they hideFirstMajorUnit/hideLastMajorUnit were set to true.

Proposed fix for: https://github.com/yui/yui3/issues/1382

Need to test:
- [x] ie6
- [x] ie7
- [x] ie8
- [x] ie9
- [x] ie10
- [x] ie11
- [x] mac safari
- [x] ios safari
- [x] android 2.3.4
- [x] android 4.1.1
- [x] firefox
- [x] chrome