Remove es6-promisify

packages/0x.js/package.json

@@ -92,7 +92,6 @@
     "bintrees": "^1.0.2",
     "bn.js": "4.11.8",
     "compare-versions": "^3.0.1",
-    "es6-promisify": "^5.0.0",
     "ethereumjs-abi": "^0.6.4",
     "ethereumjs-blockstream": "^2.0.6",
     "ethereumjs-util": "^5.1.1",

packages/0x.js/src/globals.d.ts

@@ -39,12 +39,6 @@ declare module 'compare-versions' {
     export = compareVersions;
 }
 
-// es6-promisify declarations
-declare function promisify(original: any, settings?: any): ((...arg: any[]) => Promise<any>);
-declare module 'es6-promisify' {
-    export = promisify;
-}
-
 declare module 'ethereumjs-abi' {
     const soliditySHA3: (argTypes: string[], args: any[]) => Buffer;
 }