No longer use emscripten functions for gamepads, implement them as
library functions in library_godot_display.js instead.
This allows us to do a better job at "guessing" vendorId, productId, OS,
etc. thus allowing us to better find the remapping for the controller.
The 204 and 205 are the older, SDL 2.0.4 and 2.0.5 compatible mappings,
but since all new mappings have only been added to the main
gamecontrollerdb.txt which overrides the older entries, it doesn't make
much sense for us to keep the old databases.
We do not support the SDL2 half axes and inverted axes features from
gamecontrollerdb.txt, but this only impacts the specific controllers
which can use those features, the rest are parsed and used properly.
As for godotcontrollerdb.txt, it doesn't make sense for us to maintain
our own custom mappings instead of submitting them upstream. The only
exception is the Javascript and UWP platforms for which no bindings are
available upstream, so we keep those entries.
