Remove "browser" version

Ref #18

Since the problem with uglify is fixed there is not reason to keep
browser version which do not add any benefits. Actually it blocks us
from distributing `esm` version which is widely used these days and
supported by the most popular bundlers like webpack, rollup and parcel.

Here's a few links
facebook/fbjs#86 (comment)

Both uglify and babel minify support evaulation and eliminating

```js
(function () {
  function warning() {}

  var __DEV__ = 'production' !== 'production'

  if (__DEV__) {
    warning = function (msg) {
      console.log(msg)
    }
  }

  warning()
} ());
```

https://skalman.github.io/UglifyJS-online/

https://babeljs.io/repl#?babili=true&browsers=&build=&builtIns=false&code_lz=BQMwrgdgxgLglgewgAmASmQbwFDOeaeJZAdwEMAnCOCAc3SwF9tdkA3S5AfS4BEBRAGo9kAXmQByAA4UEAEzCxEECcgCEo8dNkKlSCSzxwQqHgOFcMOPHnJUatMfkh6UwALYBnWldY3kUEieCAA2AKYAdCEI9F4-fsjMeMysdtR06NiMqGhoANxAA&debug=false&forceAllTransforms=false&shippedProposals=false&circleciRepo=&evaluate=false&fileSize=false&lineWrap=false&presets=babili%2Cenv&prettier=false&targets=&version=6.26.0&envVersion=1.6.2

Author: TrySound

browser.js

@@ -3,14 +3,12 @@
   "version": "3.0.0",
   "description": "A mirror of Facebook's Warning",
   "main": "warning.js",
-  "browser": "browser.js",
   "browserify": {
     "transform": [
       "loose-envify"
     ]
   },
   "files": [
-    "browser.js",
     "warning.js"
   ],
   "scripts": {
@@ -21,7 +19,8 @@
   },
   "devDependencies": {
     "browserify": "^11.0.1",
-    "tap": "^1.4.0"
+    "tap": "^1.4.0",
+    "uglify-js": "^3.3.25"
   },
   "repository": {
     "type": "git",

package.json

@@ -3,6 +3,7 @@
 var browserify = require('browserify');
 var test = require('tap').test;
 var vm = require('vm');
+var minify = require('uglify-js').minify;
 
 var file = __dirname + '/package/' + process.env.NODE_ENV + '.js';
 
@@ -19,8 +20,9 @@ test('browserify', function(t) {
   });
   b.bundle(function(err, src) {
     t.notOk(err);
-    t.notMatch(String(src), /\bprocess\.env\.NODE_ENV\b/);
-    t.notMatch(String(src), /__DEV__/);
+    var minified = minify(src).code
+    t.notMatch(String(minified), /\bprocess\.env\.NODE_ENV\b/);
+    t.notMatch(String(minified), /__DEV__/);
     var c = {console: {}};
     vm.runInNewContext(src, c);
     c.package(t);