Update user display to show usage days and remove expiry days column

[SeyedHashtag]

This small change updates the users display in the UI to show a user's usage days instead of their expiry days and removes the now-obsolete "expiry days" column similar to the way we show "Traffic Usage".

Replaces "Expiry days" with "Usage days" in the users table
Removes the expiry days column and any related references

This feature is tested and confirmed functioning.

[ReturnFI]

Hello and thank you for your contribution.
Did you test it in different display modes to ensure it's responsive?
Did you also test it for editing users?

[SeyedHashtag]

Yes. I've done some tests with mobile display.
I also used it for over a week to ensure it's functionality.