Migrate WorkManager to AndroidX (#1300)

Signed-off-by: mueller-ma <mueller-ma@users.noreply.github.com>

mobile/build.gradle

@@ -102,7 +102,7 @@ dependencies {
     implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
     implementation 'com.google.android.material:material:1.0.0'
     implementation 'androidx.multidex:multidex:2.0.1'
-    implementation 'android.arch.work:work-runtime:1.0.1'
+    implementation 'androidx.work:work-runtime:2.0.1'
     implementation 'org.jmdns:jmdns:3.5.5'
     implementation 'com.squareup.okhttp3:okhttp:3.12.1'
     implementation 'com.squareup.okhttp3:logging-interceptor:3.12.1'

mobile/src/main/java/org/openhab/habdroid/background/NotificationUpdateObserver.java

@@ -24,7 +24,6 @@ import org.openhab.habdroid.util.Constants;
 import org.openhab.habdroid.util.Util;
 
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;