How do I make a command in a batch file not prompt to front?

It is your use of start which causes the new window to appear.

7z is 7-Zip's command-line program, so it can be called directly:

"C:\Program Files\7-Zip\7z.exe" u ...

This way everything stays within the original window.

Use start with parameter '/B':

start /B /WAIT /d "C:\Program Files\7-Zip" 7z.exe u -ms=off "D:\7zbackup\android.7z" "C:\xampp\htdocs\android"

/b: Starts an application without opening a new command prompt window. Ctrl + C handling is ignored unless the application enables Ctrl + C processing. Use Ctrl + Break to interrupt the application. (Start (TechNet).)