Do not check errors with instanceof (#805)

This fixes cross-VM type issues in Jest.

Backport of isaacs/rimraf@aa50e02

Author: federicobozzini

lib/remove/rimraf.js

@@ -113,9 +113,6 @@ function fixWinEPERM (p, options, er, cb) {
   assert(p)
   assert(options)
   assert(typeof cb === 'function')
-  if (er) {
-    assert(er instanceof Error)
-  }
 
   options.chmod(p, 0o666, er2 => {
     if (er2) {
@@ -139,9 +136,6 @@ function fixWinEPERMSync (p, options, er) {
 
   assert(p)
   assert(options)
-  if (er) {
-    assert(er instanceof Error)
-  }
 
   try {
     options.chmodSync(p, 0o666)
@@ -173,9 +167,6 @@ function fixWinEPERMSync (p, options, er) {
 function rmdir (p, options, originalEr, cb) {
   assert(p)
   assert(options)
-  if (originalEr) {
-    assert(originalEr instanceof Error)
-  }
   assert(typeof cb === 'function')
 
   // try to rmdir first, and only readdir on ENOTEMPTY or EEXIST (SunOS)
@@ -268,9 +259,6 @@ function rimrafSync (p, options) {
 function rmdirSync (p, options, originalEr) {
   assert(p)
   assert(options)
-  if (originalEr) {
-    assert(originalEr instanceof Error)
-  }
 
   try {
     options.rmdirSync(p)