stream: remove redundant context from comments

Using the variable name in the comment and justifying the type seems
redundant to me and instead it should defined the entity which it is
acting, like in our case it is acting as a flag to control the flow in
streams.

lib/internal/streams/from.js

@@ -38,11 +38,11 @@ function from(Readable, iterable, opts) {
     ...opts
   });
 
-  // Reading boolean to protect against _read
+  // Flag to protect against _read
   // being called before last iteration completion.
   let reading = false;
 
-  // needToClose boolean if iterator needs to be explicitly closed
+  // Flag for when iterator needs to be explicitly closed.
   let needToClose = false;
 
   readable._read = function() {