Cleanup: removed some vendor-prefixed properties

The unprefixed versions can be used in the browsers we support.

Conflicts:
	pootle/static/css/login.css
	pootle/static/css/style.css
Cleanup: removed IE-specific stylesheet

Conditional comments are deprecated since IE 10.
Followup: Remove additional vendor-prefixed properties
Cleanup: Remove commented code

Was there since years ago.