chore(e2e): remove application activity from capabilities

The nativescript-dev-appium plugin gets it automatically, no need to declare it in the `appium.capabilities.json` file.

Author: vchimev

Diff for: demo/config/appium.capabilities.json

@@ -5,7 +5,6 @@
         "deviceName": "Emulator-Api19-Default",
         "avd": "Emulator-Api19-Default",
         "lt": 60000,
-        "appActivity": "org.myApp.MainActivity",
         "newCommandTimeout": 720,
         "noReset": true,
         "fullReset": false,
@@ -17,7 +16,6 @@
         "deviceName": "Emulator-Api21-Default",
         "avd": "Emulator-Api21-Default",
         "lt": 60000,
-        "appActivity": "org.myApp.MainActivity",
         "newCommandTimeout": 720,
         "noReset": true,
         "fullReset": false,
@@ -29,7 +27,6 @@
         "deviceName": "Emulator-Api23-Default",
         "avd": "Emulator-Api23-Default",
         "lt": 60000,
-        "appActivity": "org.myApp.MainActivity",
         "newCommandTimeout": 720,
         "noReset": true,
         "fullReset": false,
@@ -41,7 +38,6 @@
         "deviceName": "Emulator-Api24-Default",
         "avd": "Emulator-Api24-Default",
         "lt": 60000,
-        "appActivity": "org.myApp.MainActivity",
         "newCommandTimeout": 720,
         "noReset": true,
         "fullReset": false,
@@ -53,7 +49,6 @@
         "deviceName": "Emulator-Api25-Google",
         "avd": "Emulator-Api25-Google",
         "lt": 60000,
-        "appActivity": "org.myApp.MainActivity",
         "newCommandTimeout": 720,
         "noReset": true,
         "fullReset": false,
@@ -65,7 +60,6 @@
         "deviceName": "Emulator-Api26-Google",
         "avd": "Emulator-Api26-Google",
         "lt": 60000,
-        "appActivity": "org.myApp.MainActivity",
         "newCommandTimeout": 720,
         "noReset": true,
         "fullReset": false,
@@ -77,7 +71,6 @@
         "deviceName": "Emulator-Api27-Google",
         "avd": "Emulator-Api27-Google",
         "lt": 60000,
-        "appActivity": "org.myApp.MainActivity",
         "newCommandTimeout": 720,
         "noReset": true,
         "fullReset": false,