Remove unnecessary babel transforms

.eslintrc.js

@@ -2,7 +2,7 @@ module.exports = {
   "extends": ["eslint:recommended"],
 
   "env": {
-    "es6": true,
+    "es2018": true,
     "node": true
   },
 

scripts/babel-plugins.js

@@ -1,16 +1 @@
-module.exports = [
-  '@babel/plugin-transform-arrow-functions',
-  '@babel/plugin-transform-block-scoped-functions',
-  '@babel/plugin-transform-block-scoping',
-  '@babel/plugin-transform-classes',
-  '@babel/plugin-transform-computed-properties',
-  '@babel/plugin-transform-destructuring',
-  '@babel/plugin-transform-duplicate-keys',
-  '@babel/plugin-transform-for-of',
-  '@babel/plugin-transform-literals',
-  '@babel/plugin-transform-modules-commonjs',
-  '@babel/plugin-transform-parameters',
-  '@babel/plugin-transform-shorthand-properties',
-  '@babel/plugin-transform-spread',
-  '@babel/plugin-transform-template-literals',
-];
+module.exports = ['@babel/plugin-transform-modules-commonjs'];

src/Observable.js

@@ -1,10 +1,9 @@
 // === Symbol Support ===
 
-const hasSymbols = () => typeof Symbol === 'function';
-const hasSymbol = name => hasSymbols() && Boolean(Symbol[name]);
+const hasSymbol = name => Boolean(Symbol[name]);
 const getSymbol = name => hasSymbol(name) ? Symbol[name] : '@@' + name;
 
-if (hasSymbols() && !hasSymbol('observable') && Object.isExtensible(Symbol)) {
+if (!hasSymbol('observable') && Object.isExtensible(Symbol)) {
   Symbol.observable = Symbol('observable');
 }
 
@@ -464,12 +463,10 @@ export class Observable {
 
 }
 
-if (hasSymbols()) {
-  Object.defineProperty(Observable, Symbol('extensions'), {
-    value: {
-      symbol: SymbolObservable,
-      hostReportError,
-    },
-    configurable: true,
-  });
-}
+Object.defineProperty(Observable, Symbol('extensions'), {
+  value: {
+    symbol: SymbolObservable,
+    hostReportError,
+  },
+  configurable: true,
+});