Cleanup emSetImmediate/emClearImmediate. NFC (emscripten-core#22890)

This change avoids the extra dummy library entry `polyfillSetImmediate`.

Author: sbc100

src/library_eventloop.js

@@ -52,10 +52,8 @@ LibraryJSEventLoop = {
     setImmediateWrapped.mapping[id] = undefined;
   },
 
-  $polyfillSetImmediate__deps: ['$setImmediateWrapped', '$clearImmediateWrapped'],
-  $polyfillSetImmediate__postset: `
-    var emSetImmediate;
-    var emClearImmediate;
+  $emSetImmediate__deps: ['$setImmediateWrapped', '$clearImmediateWrapped', '$emClearImmediate'],
+  $emSetImmediate__postset: `
     if (typeof setImmediate != "undefined") {
       emSetImmediate = setImmediateWrapped;
       emClearImmediate = clearImmediateWrapped;
@@ -82,14 +80,12 @@ LibraryJSEventLoop = {
         if (index >= 0 && index < __setImmediate_queue.length) __setImmediate_queue[index] = () => {};
       })
     }`,
+  $emSetImmediate: undefined,
 
-  $polyfillSetImmediate: () => {
-    // nop, used for its postset to ensure setImmediate() polyfill is
-    // not duplicated between emscripten_set_immediate() and
-    // emscripten_set_immediate_loop() if application links to both of them.
-  },
+  $emClearImmediate_deps: ['$emSetImmediate'],
+  $emClearImmediate: undefined,
 
-  emscripten_set_immediate__deps: ['$polyfillSetImmediate', '$callUserCallback'],
+  emscripten_set_immediate__deps: ['$emSetImmediate', '$callUserCallback'],
   emscripten_set_immediate: (cb, userData) => {
     {{{ runtimeKeepalivePush(); }}}
     return emSetImmediate(() => {
@@ -98,13 +94,13 @@ LibraryJSEventLoop = {
     });
   },
 
-  emscripten_clear_immediate__deps: ['$polyfillSetImmediate'],
+  emscripten_clear_immediate__deps: ['$emClearImmediate'],
   emscripten_clear_immediate: (id) => {
     {{{ runtimeKeepalivePop(); }}}
     emClearImmediate(id);
   },
 
-  emscripten_set_immediate_loop__deps: ['$polyfillSetImmediate', '$callUserCallback'],
+  emscripten_set_immediate_loop__deps: ['$emSetImmediate', '$callUserCallback'],
   emscripten_set_immediate_loop: (cb, userData) => {
     function tick() {
       callUserCallback(() => {

test/other/codesize/test_codesize_hello_O0.gzsize

@@ -1 +1 @@
-7905
+7913

test/other/codesize/test_codesize_hello_O0.jssize

@@ -1 +1 @@
-21012
+21045

test/other/codesize/test_codesize_minimal_O0.gzsize

@@ -1 +1 @@
-6443
+6449

test/other/codesize/test_codesize_minimal_O0.jssize

@@ -1 +1 @@
-17061
+17094

test/other/test_unoptimized_code_size.js.size

@@ -1 +1 @@
-52855
+52898

test/other/test_unoptimized_code_size_strict.js.size

@@ -1 +1 @@
-51638
+51681