Don't expose deno_buf from core

[bartlomieju]

Closes #2076.

I also modified comment that was outdated.

[ry]

Thanks! Can you also include this change:

commit 6e3b442ddcd6cda997930540577f6390ee7f8ccf
Author: Ryan Dahl <ry@tinyclouds.org>
Date:   Thu May 9 10:20:34 2019 -0400

    core: Privatize ModuleNameMap and SymbolicModule

diff --git a/core/modules.rs b/core/modules.rs
index 0e7cc68a..0fb3147c 100644
--- a/core/modules.rs
+++ b/core/modules.rs
@@ -305,7 +305,7 @@ impl ModuleInfo {
 }
 
 /// A symbolic module entity.
-pub enum SymbolicModule {
+enum SymbolicModule {
   /// This module is an alias to another module.
   /// This is useful such that multiple names could point to
   /// the same underlying module (particularly due to redirects).
@@ -316,7 +316,7 @@ pub enum SymbolicModule {
 
 #[derive(Default)]
 /// Alias-able module name map
-pub struct ModuleNameMap {
+struct ModuleNameMap {
   inner: HashMap<String, SymbolicModule>,
 }
 

[ry]

LGTM