Bug 1092388 - Remove cross-origin document.write test. r=bz, a=2.1+

This test is pretty bogus. It uses enablePrivilege and then tries to test
various document.write behaviors across origins.

This test in general is pretty terrible. I spent a while trying to improve it,
got frustrated, was tempted to remove the whole thing, and then finally settled
on this as the path of least resistance.
Bug 1092388 - Clamp the entry and incumbent global to the current global if their principals don't match. r=bz, a=2.1+
Bug 1092388 - Remove now-unnecessary nsGlobalWindow::CallerGlobal. r=bz, a=2.1+
Bug 984467 - Remove current inner fallback in CallerInnerWindow. r=bz, a=bajaj