Maybe remove Ninja from tor-browser-build

So I investigated this a little bit a year or so ago when re-writing ricochet-build. As far as I could tell, Ninja was only being used as a target for CMake (i.e. CMake would generate ninja build files, then we'd use ninja to build). From my reading back then, Ninja's primary benefit over alternatives is in smarter/faster incremental builds. So if you're doing active development, your edit+build+test loop is faster. However, all of our builds in tor-browser-build are full, so we're not actually seeing any benefit to this with the tradeoff of additional complexity.

I would additionally propose that for the projects which do use CMake, that we just build with it directly rather than generating some other build scripts (i.e. via cmake --build and cmake --install)