Remove `SDL_DROPEVENT_DATA_SIZE` and `SDL_TEXTEDITINGEVENT_TEXT_SIZE`

[icculus]

Both of these are still in SDL_events.h, but (afaik?) these buffers are now unlimited in size.

SDL_DROPEVENT_DATA_SIZE is unused internally in SDL at this point, but there are a few references to SDL_TEXTEDITINGEVENT_TEXT_SIZE in the source still that are using it (incorrectly?).

[slouken]

Nope, they're not needed.