shell.js: Remove moduleOverrides. NFC (emscripten-core#23991)

This mechanism was added back in 80f517d so that shell code could
unconditionally assign to the `Module` object without clobbering the
incoming values there.

These days the shell code no longer assigns to the Module object so it
is no longer necessary.

Basically this code protects against accidental assignments to `Module`
between lines 138 and 408, but we don't have any such assignments that I
can see in our code.

Author: sbc100

src/shell.js

@@ -129,13 +129,6 @@ var ENVIRONMENT_IS_WASM_WORKER = !!Module['$ww'];
 // refer to Module (if they choose; they can also define Module)
 {{{ preJS() }}}
 
-// Sometimes an existing Module object exists with properties
-// meant to overwrite the default module functionality. Here
-// we collect those properties and reapply _after_ we configure
-// the current environment's defaults to avoid having to be so
-// defensive during initialization.
-var moduleOverrides = {...Module};
-
 var arguments_ = [];
 var thisProgram = './this.program';
 var quit_ = (status, toThrow) => {
@@ -218,9 +211,8 @@ if (ENVIRONMENT_IS_NODE) {
 
   arguments_ = process.argv.slice(2);
 
-#if MODULARIZE
+#if !MODULARIZE
   // MODULARIZE will export the module in the proper place outside, we don't need to export here
-#else
   if (typeof module != 'undefined') {
     module['exports'] = Module;
   }
@@ -406,11 +398,6 @@ if (ENVIRONMENT_IS_NODE) {
 {{{ makeModuleReceiveWithVar('err', 'printErr', 'console.error.bind(console)', true) }}}
 #endif
 
-// Merge back in the overrides
-Object.assign(Module, moduleOverrides);
-// Free the object hierarchy contained in the overrides, this lets the GC
-// reclaim data used.
-moduleOverrides = null;
 #if ASSERTIONS
 checkIncomingModuleAPI();
 #endif

test/browser/test_small_js_flags.js.size

@@ -1 +1 @@
-4133
+4091

test/other/codesize/test_codesize_cxx_ctors1.gzsize

@@ -1 +1 @@
-8240
+8223

test/other/codesize/test_codesize_cxx_ctors1.jssize

@@ -1 +1 @@
-19983
+19945

test/other/codesize/test_codesize_cxx_ctors2.gzsize

@@ -1 +1 @@
-8229
+8212

test/other/codesize/test_codesize_cxx_ctors2.jssize

@@ -1 +1 @@
-19961
+19923

test/other/codesize/test_codesize_cxx_except.gzsize

@@ -1 +1 @@
-9240
+9221

test/other/codesize/test_codesize_cxx_except.jssize

@@ -1 +1 @@
-23720
+23682

test/other/codesize/test_codesize_cxx_except_wasm.gzsize

@@ -1 +1 @@
-8189
+8167

test/other/codesize/test_codesize_cxx_except_wasm.jssize

@@ -1 +1 @@
-19875
+19837