Remove skipTest from canvas_animate_resize. NFC (#24855)

Rather than magically skipping the test when OffscreenCanvas is not
supported we should just fail.

If folks want to run the whole test suite on a browser without such
support we can add an `EMTEST_SKIP_OFFSCREEN_CANVAS` environment
variable to control if/when these tests are run.

I don't think this should be needed though since modern browsers all
support `OffscreenCanvas`.

See #24854

Author: sbc100

test/canvas_animate_resize.c

@@ -114,23 +114,15 @@ void init() {
   glLinkProgram(program);
 }
 
-int main()
-{
+int main() {
   EmscriptenWebGLContextAttributes attr;
   emscripten_webgl_init_context_attributes(&attr);
 #if TEST_EXPLICIT_CONTEXT_SWAP
   attr.explicitSwapControl = true;
 #endif
   ctx = emscripten_webgl_create_context("#canvas", &attr);
   printf("Created context with handle %#lx\n", ctx);
-  if (!ctx) {
-    if (!emscripten_supports_offscreencanvas()) {
-      EM_ASM({
-        skipTest('OffscreenCanvas is not supported!');
-      });
-    }
-    return 0;
-  }
+  assert(ctx);
   emscripten_webgl_make_context_current(ctx);
 
   init();