Prevent esm module from being loaded by default

The module hadn't been suffciently tested and wasn't completely
consistent with the main module. It should not yet be the default. It
can still be manually imported if desired.

Author: blazzy

package.json

@@ -10,7 +10,6 @@
   ],
   "repository": "git://github.com/amplitude/amplitude-javascript.git",
   "main": "amplitude.js",
-  "module": "amplitude.esm.js",
   "react-native": "amplitude.native.js",
   "dependencies": {
     "@amplitude/ua-parser-js": "0.7.20",