fs: use process.emitWarning to print deprecation warning

As an alternative to nodejs#6413, use
process.emitWarning() instead of the internal printDeprecationMessage
in order to avoid use of an internal only API.

lib/fs.js

@@ -43,7 +43,6 @@ const isWindows = process.platform === 'win32';
 
 const DEBUG = process.env.NODE_DEBUG && /fs/.test(process.env.NODE_DEBUG);
 const errnoException = util._errnoException;
-const printDeprecation = require('internal/util').printDeprecationMessage;
 
 function throwOptionsError(options) {
   throw new TypeError('Expected options to be either an object or a string, ' +
@@ -613,10 +612,14 @@ var readWarned = false;
 fs.read = function(fd, buffer, offset, length, position, callback) {
   if (!(buffer instanceof Buffer)) {
     // legacy string interface (fd, length, position, encoding, callback)
-    readWarned = printDeprecation('fs.read\'s legacy String interface ' +
-                                  'is deprecated. Use the Buffer API as ' +
-                                  'mentioned in the documentation instead.',
-                                  readWarned);
+    if (!readWarned) {
+      readWarned = true;
+      process.emitWarning(
+        'fs.read\'s legacy String interface is deprecated. Use the Buffer ' +
+        'API as mentioned in the documentation instead.',
+        'DeprecationWarning');
+    }
+
     const cb = arguments[4];
     const encoding = arguments[3];
 
@@ -673,10 +676,13 @@ fs.readSync = function(fd, buffer, offset, length, position) {
 
   if (!(buffer instanceof Buffer)) {
     // legacy string interface (fd, length, position, encoding, callback)
-    readSyncWarned = printDeprecation('fs.readSync\'s legacy String interface' +
-                                      'is deprecated. Use the Buffer API as ' +
-                                      'mentioned in the documentation instead.',
-                                      readSyncWarned);
+    if (!readSyncWarned) {
+      readSyncWarned = true;
+      process.emitWarning(
+        'fs.readSync\'s legacy String interface is deprecated. Use the ' +
+        'Buffer API as mentioned in the documentation instead.',
+        'DeprecationWarning');
+    }
     legacy = true;
     encoding = arguments[3];