Bug 1540990 - Get rid of unnecessary nsIPresShell.h inclusions r=emilio

A lot of files include `nsIPresShell.h` even though currently they don't
need it.  This patch removes the unnecessary inclusions.

Differential Revision: https://phabricator.services.mozilla.com/D25744

dom/html/HTMLBodyElement.cpp

@@ -13,7 +13,6 @@
 #include "nsGkAtoms.h"
 #include "nsStyleConsts.h"
 #include "nsPresContext.h"
-#include "nsIPresShell.h"
 #include "mozilla/dom/Document.h"
 #include "DocumentInlines.h"
 #include "nsHTMLStyleSheet.h"