Move debug check from doWork

[nya-elimu]

In UploadEventsWorker, the code only gets executed if the current build type is not "debug":

if (!"debug".equals(BuildConfig.BUILD_TYPE)) {
    uploadLetterLearningEvents();
    uploadLetterAssessmentEvents();
    uploadWordLearningEvents();
    uploadWordAssessmentEvents();
    uploadStoryBookLearningEvents();
}

A better solution would be to execute as much code as possible, and skipping execution at the point where the files are about to get uploaded to the server. This way, a larger part of the code gets executed (and tested) during development, also making debugging easier.