Remap:

Tab and Backspace trigger the same key code (42).
They are going to be the tab,
while Del (Keycode 71) will be the backspace.
Remap:

1. Tab to Tab as previous commit
2. Backspace to KEYPAD_9
3. KEYPAD_CLEAR to KEYPAD_9

-> Backspace and Tab will be Tab
-> Del/M4 will be backspace