Update compileSDK in app/build.gradle and remove dependency

- updated compileSdkVersion from 28 to 31 to allow WorkManager API support
- removed dependency: implementation 'com.android.support:appcompat-v7:26.1.0' because
it is useless in our scope. As stated at https://developer.android.com/topic/libraries/support-library/packages#v7-appcompat
it only add ActionBar relative code. But eDrive doesn't use it for a while.