Remove redundant code

That one was needed for Node.js 0.9.4 and below,
which is not supported anymore.

package.json

@@ -45,7 +45,6 @@
     "performance-now": "^2.1.0",
     "qs": "~6.5.1",
     "safe-buffer": "^5.1.1",
-    "stringstream": "~0.0.5",
     "tough-cookie": "~2.3.3",
     "tunnel-agent": "^0.6.0",
     "uuid": "^3.1.0"

request.js

@@ -11,7 +11,6 @@ var aws2 = require('aws-sign2')
 var aws4 = require('aws4')
 var httpSignature = require('http-signature')
 var mime = require('mime-types')
-var stringstream = require('stringstream')
 var caseless = require('caseless')
 var ForeverAgent = require('forever-agent')
 var FormData = require('form-data')
@@ -1049,13 +1048,8 @@ Request.prototype.onRequestResponse = function (response) {
     if (self.encoding) {
       if (self.dests.length !== 0) {
         console.error('Ignoring encoding parameter as this stream is being piped to another stream which makes the encoding option invalid.')
-      } else if (responseContent.setEncoding) {
-        responseContent.setEncoding(self.encoding)
       } else {
-        // Should only occur on node pre-v0.9.4 (joyent/node@9b5abe5) with
-        // zlib streams.
-        // If/When support for 0.9.4 is dropped, this should be unnecessary.
-        responseContent = responseContent.pipe(stringstream(self.encoding))
+        responseContent.setEncoding(self.encoding)
       }
     }