Remove stream subprovider

Since the polling leak seems to be coming from elsewhere, and new bugs came from this, I'm rolling back this change so that we can push the other improvements sooner and fix the bug at its true root.

app/scripts/lib/inpage-provider.js

@@ -1,7 +1,5 @@
 const pipe = require('pump')
-const ProviderEngine = require('web3-provider-engine')
-const FilterSubprovider = require('web3-provider-engine/subproviders/filters')
-const StreamSubprovider = require('web3-provider-engine/subproviders/stream')
+const StreamProvider = require('web3-stream-provider')
 const LocalStorageStore = require('obs-store')
 const ObjectMultiplex = require('./obj-multiplex')
 const createRandomId = require('./random-id')
@@ -29,24 +27,14 @@ function MetamaskInpageProvider (connectionStream) {
   )
 
   // connect to async provider
-  const engine = new ProviderEngine()
-
-  const filterSubprovider = new FilterSubprovider()
-  engine.addProvider(filterSubprovider)
-
-  const streamSubprovider = new StreamSubprovider()
-  engine.addProvider(streamSubprovider)
-
+  const asyncProvider = self.asyncProvider = new StreamProvider()
   pipe(
-    streamSubprovider,
+    asyncProvider,
     multiStream.createStream('provider'),
-    streamSubprovider,
+    asyncProvider,
     (err) => logStreamDisconnectWarning('MetaMask RpcProvider', err)
   )
-
   // start and stop polling to unblock first block lock
-  engine.start()
-  engine.once('latest', () => engine.stop())
 
   self.idMap = {}
   // handle sendAsync requests via asyncProvider
@@ -59,7 +47,7 @@ function MetamaskInpageProvider (connectionStream) {
       return message
     })
     // forward to asyncProvider
-    engine.sendAsync(request, function (err, res) {
+    asyncProvider.sendAsync(request, function (err, res) {
       if (err) return cb(err)
       // transform messages to original ids
       eachJsonMessage(res, (message) => {