The die() API for abnormal termination does not belong within the core
of netsurf and instead errors are propogated back to the callers.
This is the final part of this change and the API is now only used within
some parts of the frontends
The netsurf.h header should *only* contain the registration, core
initialisation and finalisation methods. Version information is best
placed in its own header.
Also remove any unneeded inclusion of this header limiting it to
solely the places the relevant API is required.
