[emscripten] Remove referenc to Module['createContext']

The Module interface is the one used by the outside world.  This code
is inside the module itself so can use the internal name, avoiding the
need to export this function on the Module at all.

See https://github.com/emscripten-core/emscripten/pull/24269

src/video/emscripten/SDL_emscriptenframebuffer.c

@@ -78,7 +78,7 @@ bool Emscripten_UpdateWindowFramebuffer(SDL_VideoDevice *_this, SDL_Window *wind
         if (!Module['SDL3']) Module['SDL3'] = {};
         var SDL3 = Module['SDL3'];
         if (SDL3.ctxCanvas !== canvas) {
-            SDL3.ctx = Module['createContext'](canvas, false, true);
+            SDL3.ctx = Browser.createContext(canvas, false, true);
             SDL3.ctxCanvas = canvas;
         }
         if (SDL3.w !== w || SDL3.h !== h || SDL3.imageCtx !== SDL3.ctx) {