hidden-* doesn't change display of visibles

Removed ```.responsive-visibility();``` from ```hidden-*``` classes.

All test cases under http://getbootstrap.com/css/#responsive-utilities are passing, and now we can use ```hidden-*``` classes on non-block elements.

e.g. http://jsbin.com/odEcaXE/3/edit

This way we don't have to add support for all tags.

X-Ref: #8869

What you think?