re-enabled x-metamask-origin for mascara

app/scripts/metamask-controller.js

@@ -196,7 +196,7 @@ module.exports = class MetamaskController extends EventEmitter {
       },
       // rpc data source
       rpcUrl: this.networkController.getCurrentRpcAddress(),
-      originHttpHeaderKey: this.platform.isExtension ? 'X-Metamask-Origin' : undefined,
+      originHttpHeaderKey: 'X-Metamask-Origin',
       // account mgmt
       getAccounts: (cb) => {
         const isUnlocked = this.keyringController.memStore.getState().isUnlocked

app/scripts/platforms/extension.js

@@ -5,10 +5,6 @@ class ExtensionPlatform {
   //
   // Public
   //
-  get isExtension () {
-    return true
-  }
-
   reload () {
     extension.runtime.reload()
   }