MainApp: remove unused variable

Leftover

Signed-off-by: Álvaro Brey Vilas <alvaro.brey@nextcloud.com>

app/src/main/java/com/owncloud/android/MainApp.java

@@ -231,7 +231,6 @@ public class MainApp extends MultiDexApplication implements HasAndroidInjector {
         // we don't want to handle crashes occurring inside crash reporter activity/process;
         // let the platform deal with those
         final boolean isCrashReportingProcess = getAppProcessName().endsWith(":crash");
-        final boolean useExceptionHandler = !appInfo.isDebugBuild();
 
         if (!isCrashReportingProcess && !appInfo.isDebugBuild()) {
             Thread.UncaughtExceptionHandler defaultPlatformHandler = Thread.getDefaultUncaughtExceptionHandler();