Improve backup display names with emulated storage

-Change backup display name to say that we are excluding storage
-Add warning message during backup of any partition with data media
-Also eliminate unused variable from twrpTar class

Maybe this will make the people in issue 276 happy, but probably not because
they already lost their data, or because the warning text is yellow instead of
red.
https://github.com/TeamWin/Team-Win-Recovery-Project/issues/276

Change-Id: I98303fe7f6b7a25fea029637c90145258d41ee46
diff --git a/gui/theme/common/languages/en.xml b/gui/theme/common/languages/en.xml
index d911312..72ef5af 100644
--- a/gui/theme/common/languages/en.xml
+++ b/gui/theme/common/languages/en.xml
@@ -19,6 +19,7 @@
 		<string name="recovery">Recovery</string>
 		<string name="cache">Cache</string>
 		<string name="data">Data</string>
+		<string name="data_backup">Data (excl. storage)</string>
 		<string name="sdcard">SDCard</string>
 		<string name="internal">Internal Storage</string>
 		<string name="microsd">Micro SDCard</string>
@@ -595,6 +596,7 @@
 		<string name="remove_all">Removing all files under '{1}'</string>
 		<string name="wiping_data">Wiping data without wiping /data/media ...</string>
 		<string name="backing_up">Backing up {1}...</string>
+		<string name="backup_storage_warning">Backups of {1} do not include any files in internal storage such as pictures or downloads.</string>
 		<string name="backing">Backing Up</string>
 		<string name="backup_size">Backup file size for '{1}' is 0 bytes.</string>
 		<string name="datamedia_fs_restore">WARNING: This /data backup was made with {1} file system! The backup may not boot unless you change back to {1}.</string>