Remove unused file.

src/core/PromiseWaiter.js

@@ -1,41 +0,0 @@
-/**
- * Wait for multiple Promises to resolve.
- */
-module.exports = class PromiseWaiter {
-  constructor () {
-    this.promises = []
-  }
-
-  add (promise) {
-    this.promises.push(promise)
-
-    const remove = () => {
-      this.remove(promise)
-    }
-    promise.then(remove, remove)
-  }
-
-  remove (promise) {
-    const index = this.promises.indexOf(promise)
-    if (index !== -1) {
-      this.promises.splice(index, 1)
-    }
-  }
-
-  wait () {
-    const promises = this.promises
-    this.promises = []
-
-    function noop () {
-      // No result value
-    }
-
-    // Just wait for a Promise to conclude in some way, whether it's resolution
-    // or rejection. We don't care about the contents.
-    function concluded (promise) {
-      return promise.then(noop, noop)
-    }
-
-    return Promise.all(promises.map(concluded)).then(noop)
-  }
-}