Bug 1514936, part 1 - Remove the outer argument to nsIFactory::createInstance. r=xpcom-reviewers,preferences-reviewers,nika,Gijs

This patch won't actually build, because a few bits of code are used
for both nsIFactory::createInstance and static components, and static
components are not fixed until the next patch.

The first place is nsLoadGroupConstructor, which uses an nsIFactory
macro to create a static component constructor. (This could be worked
around by expanding the macro to the state before this patch.)

The other issue is that nsAppShellConstructor is used in an nsIFactory
on OSX, but as a static component on all other platforms. This could
be worked around by wrapping nsAppShellConstructor in an adaptor that
passes in the extra null argument to nsAppShellConstructor.

Differential Revision: https://phabricator.services.mozilla.com/D146456