Remove corejs, let consuming app choose which polyfills to use

babel.config.js

@@ -1,13 +1,6 @@
 const presets = [
   [
-    '@babel/env',
-    {
-      targets: {
-        browsers: ['last 2 versions', '> 5%', 'ie 9-11'],
-      },
-      useBuiltIns: 'usage',
-      corejs: '2.6'
-    },
+    '@babel/env'
   ],
 ];
 

package.json

@@ -32,7 +32,6 @@
     "@babel/preset-env": "^7.5.4",
     "@pika/plugin-build-web": "^0.3.10",
     "@pika/plugin-standard-pkg": "^0.3.10",
-    "core-js": "^2.6.3",
     "jest": "^24.8.0",
     "npm": "^6.8.0",
     "prettier": "^1.18.2"

yarn.lock

@@ -2086,11 +2086,6 @@ [email protected]:
   resolved "https://registry.yarnpkg.com/core-js-pure/-/core-js-pure-3.1.4.tgz#5fa17dc77002a169a3566cc48dc774d2e13e3769"
   integrity sha512-uJ4Z7iPNwiu1foygbcZYJsJs1jiXrTTCvxfLDXNhI/I+NHbSIEyr548y4fcsCEyWY0XgfAG/qqaunJ1SThHenA==
 
-core-js@^2.6.3:
-  version "2.6.3"
-  resolved "https://registry.yarnpkg.com/core-js/-/core-js-2.6.3.tgz#4b70938bdffdaf64931e66e2db158f0892289c49"
-  integrity sha512-l00tmFFZOBHtYhN4Cz7k32VM7vTn3rE2ANjQDxdEN6zmXZ/xq1jQuutnmHvMG1ZJ7xd72+TA5YpUK8wz3rWsfQ==
-
 [email protected], core-util-is@~1.0.0:
   version "1.0.2"
   resolved "https://registry.yarnpkg.com/core-util-is/-/core-util-is-1.0.2.tgz#b5fd54220aa2bc5ab57aab7140c940754503c1a7"