just use importobj term directly

Author: guybedford

doc/api/esm.md

@@ -717,13 +717,9 @@ into a new instance of `library.wasm`:
 ```js
 import source libraryModule from './library.wasm';
 
-const instance1 = await WebAssembly.instantiate(libraryModule, {
-  custom: import1,
-});
+const instance1 = await WebAssembly.instantiate(libraryModule, importObject1);
 
-const instance2 = await WebAssembly.instantiate(libraryModule, {
-  custom: import2,
-});
+const instance2 = await WebAssembly.instantiate(libraryModule, importObject2);
 ```
 
 In addition to the static source phase, there is also a dynamic variant of the
@@ -732,9 +728,7 @@ source phase via the `import.source` dynamic phase import syntax:
 ```js
 const dynamicLibrary = await import.source('./library.wasm');
 
-const instance = await WebAssembly.instantiate(dynamicLibrary, {
-  custom: importObj,
-});
+const instance = await WebAssembly.instantiate(dynamicLibrary, importObject);
 ```
 
 <i id="esm_experimental_top_level_await"></i>