Remove unused string, fix improperly formatted Slovak string

app/src/main/res/values-sk/strings.xml

@@ -283,7 +283,7 @@
     <string name="manga_removed_library">Odstránené z knižnice</string>
     <string name="delete_downloads_for_manga">Odstrániť stiahnuté kapitoly\?</string>
     <string name="copied_to_clipboard">%1$s bol skopírovaný do schránky</string>
-    <string name="source_not_installed">Zdroj nie je nainštalovaný</string>
+    <string name="source_not_installed">Zdroj nie je nainštalovaný: %1$s</string>
     <string name="manga_chapters_tab">Kapitoly</string>
     <string name="manga_chapter_no_title">Bez názvu</string>
     <string name="display_mode_chapter">Kapitola %1$s</string>

app/src/main/res/values/strings.xml

@@ -641,7 +641,6 @@
     <!-- File Picker Titles -->
     <string name="file_select_cover">Select cover image</string>
     <string name="file_select_backup">Select backup file</string>
-    <string name="file_select_icon">Select shortcut icon</string>
 
     <!--UpdateCheck-->
     <string name="update_check_confirm">Download</string>