[Keyboard] QWERTYYdox refactor (#6446)

* Delete null key

`__` key in keymap.c doesn't actually exist on the physical hardware.
Removed key from keymap.c and removed its argument from the layout macro.

* Delete unused keycode aliases

* Replace layer index definitions with an enum

* Replace redundant numpad keycodes with native aliases

* Use native layer change keycodes instead of aliases

* Visually align the keycodes

It makes the keymap pretty.

* Correct Configurator layout data

* Clean up header files

- convert to pragma once include guard
- remove redundant definitions
- remove commented code blocks

* Delete LAYOUT_kc macro

Was copied from ergotravel; not valid for this keyboard.

* Consolidate rev1 rules.mk settings to keyboard level

Previous codebase enabled Backlight at keyboard level then disabled it at revision level.

* Delete unused rules

* Consolidate config.h settings from keymap level to keyboard level

* Modernize keyboard's config.h file

Aligns the keyboard-level config.h file more closely with the current QMK template for AVR keyboards.

keyboards/qwertyydox/rules.mk

@@ -52,14 +52,12 @@ EXTRAKEY_ENABLE = no       # Audio control and System control(+450)
 CONSOLE_ENABLE = no         # Console for debug(+400)
 COMMAND_ENABLE = no        # Commands for debug and configuration
 NKRO_ENABLE = no            # Nkey Rollover - if this doesn't work, see here: https://github.com/tmk/tmk_keyboard/wiki/FAQ#nkro-doesnt-work
-BACKLIGHT_ENABLE = yes      # Enable keyboard backlight functionality
+BACKLIGHT_ENABLE = no      # Enable keyboard backlight functionality
 MIDI_ENABLE = no            # MIDI controls
 AUDIO_ENABLE = no           # Audio output on port C6
 UNICODE_ENABLE = no         # Unicode
 BLUETOOTH_ENABLE = no       # Enable Bluetooth with the Adafruit EZ-Key HID
 RGBLIGHT_ENABLE = no       # Enable WS2812 RGB underlight.
-SUBPROJECT_rev1 = yes
-USE_I2C = yes               # I2C is used between the sides
 # Do not enable SLEEP_LED_ENABLE. it uses the same timer as BACKLIGHT_ENABLE
 SLEEP_LED_ENABLE = no    # Breathing sleep LED during USB suspend