stream: remove dead code

This condition could never be met because all calling functions
guarded against this.

PR-URL: #15665
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/_stream_readable.js

@@ -1040,11 +1040,6 @@ function copyFromBuffer(n, list) {
 function endReadable(stream) {
   var state = stream._readableState;
 
-  // If we get here before consuming all the bytes, then that is a
-  // bug in node.  Should never happen.
-  if (state.length > 0)
-    throw new Error('"endReadable()" called on non-empty stream');
-
   if (!state.endEmitted) {
     state.ended = true;
     process.nextTick(endReadableNT, state, stream);