Bug 1792574, part 3 - Don't include nsMemory where it isn't needed. r=xpcom-reviewers,necko-reviewers,valentin,nika

There are only 3 places where nsMemory.h is still needed (image/RasterImage.cpp,
gfx/thebes/gfxFT2FontList.cpp, and nsMemory.cpp). Remove the rest.

Differential Revision: https://phabricator.services.mozilla.com/D158213