Remove unused translations without default string

  
    Lint shows the next warnings about unused translations.
    If you are not planning to use them, this commit removes the transtations
    (Or add default strings, so there are less risks and clear warnings)
    
    :android:processDebugResources
    warning: string 'navdrawer_description_a11y' has no default translation.
    warning: string 'navdrawer_item_app_feedback' has no default translation.
    warning: string 'navdrawer_item_app_feedback_a11y' has no default translation.
    warning: string 'schedule_session_subtitle' has no default translation.
    warning: string 'title_stream' has no default translation.
    warning: string 'schedule_session_subtitle' has no deafult transtation.