Avoid outputting shell code when !ENVIRONMENT_MAY_BE_SHELL. NFC (#21565)

Author: sbc100

src/shell.js

@@ -282,6 +282,7 @@ if (ENVIRONMENT_IS_SHELL) {
   if ((typeof process == 'object' && typeof require === 'function') || typeof window == 'object' || typeof importScripts == 'function') throw new Error('not compiled for this environment (did you build to HTML and try to run it not on the web, or set ENVIRONMENT to something - like node - and run it someplace else - like on the web?)');
 #endif
 
+#if ENVIRONMENT_MAY_BE_SHELL
   if (typeof read != 'undefined') {
     read_ = read;
   }
@@ -352,9 +353,10 @@ if (ENVIRONMENT_IS_SHELL) {
     eval(read(locateFile('{{{ TARGET_BASENAME }}}.wasm.js'))+'');
   }
 #endif
+#endif // ENVIRONMENT_MAY_BE_SHELL
 
 } else
-#endif // ENVIRONMENT_MAY_BE_SHELL
+#endif // ENVIRONMENT_MAY_BE_SHELL || ASSERTIONS
 
 // Note that this includes Node.js workers when relevant (pthreads is enabled).
 // Node.js workers are detected as a combination of ENVIRONMENT_IS_WORKER and

test/other/metadce/test_metadce_hello_O0.gzsize

@@ -1 +1 @@
-8337
+8114

test/other/metadce/test_metadce_hello_O0.jssize

@@ -1 +1 @@
-22876
+21940

test/other/metadce/test_metadce_minimal_O0.gzsize

@@ -1 +1 @@
-6854
+6704

test/other/metadce/test_metadce_minimal_O0.jssize

@@ -1 +1 @@
-18720
+18068

test/other/test_unoptimized_code_size.js.size

@@ -1 +1 @@
-57832
+55484

test/other/test_unoptimized_code_size_strict.js.size

@@ -1 +1 @@
-56735
+54387