Legacy: remove unused style rules for floatleft/right

Legacy: remove unused style rules for floatleft/right

These rules for paragraphs inside floatleft/right to have font-style
italic were copied in in 2004 in commit e285b0b5f1b20637e40ef789b99fc06614d92d91

But as far as I can tell they were never in use and definetly no
longer are. From core we use these classes solely to align inline
images (or these days renderer File transclusions). But as far as I
can tell no where do these feature <p> (intentionally).

Time to get rid of it I think.

Change-Id: I6f70466def688d0cb671909c71eba566ff4a4a9b