Remove injected APP_ROOT as this may change after build

For example CI servers don't have same build path as final production server path

src/webpack/ConfigFactory.js

@@ -729,8 +729,6 @@ function ConfigFactory({ target, mode, root = CWD, ...options })
         // builds as React relies on process.env.NODE_ENV for optimizations.
         "process.env.NODE_ENV": JSON.stringify(process.env.NODE_ENV),
 
-        "process.env.APP_ROOT": JSON.stringify(path.resolve(root)),
-
         // All the below items match the config items in our .env file. Go
         // to the .env.example for a description of each key.
         "process.env.SERVER_PORT": process.env.SERVER_PORT,