Remove duplicate docs about main module

doc/api/modules.markdown

@@ -350,23 +350,6 @@ The example module above could be structured like so:
   Node executes the callback immediately, so please plan your programs
   accordingly.
 
-
-### Accessing the main module
-
-When a file is run directly from Node, `require.main` is set to its
-`module`. That means that you can determine whether a file has been run
-directly by testing
-
-    require.main === module
-
-For a file `foo.js`, this will be `true` if run via `node foo.js`, but
-`false` if run by `require('./foo')`.
-
-Because `module` provides a `filename` property (normally equivalent to
-`__filename`), the entry point of the current application can be obtained
-by checking `require.main.filename`.
-
-
 ## Addenda: Package Manager Tips
 
 The semantics of Node's `require()` function were designed to be general