Change the Helix keyboard to use split_common.

[mtei]

The Helix keyboard was created before the advent of split_common, and its implementation was derived from Let's split. An implementation that uses split_common on a trial basis was also added in May 2020, allowing it to be switched as an option. (#7718)

Now that split_common has matured, we decided to use split_common entirely and remove the previous implementation.

Change procedure

• Helix/rev1 (Remove Helix/rev1 #16389)
  • remove
• Helix/pico (Helix/pico move to split_common #16418)
  • Changed to use split_common.
  • All the keymaps were tested and confirmed to work.
• Helix/rev2
  • Step1
    • Switch the 'default' keymap setting to use split_common. (Change 'helix/rev2:default' setting to use split_common #16432)
    • Switch the "led_test' keymap setting to use split_common. (Change 'helix/rev2:default' setting to use split_common #16432)
    • Switch the 'five_rows' keymap setting to use split_common. (Change 'helix/rev2:default' setting to use split_common #16432)
    • Switch the 'edvorakjp' keymap setting to use split_common. (Change helix:edvorakjp keymap to use split_common #16532)
    • Switch the 'fraanrosi' keymap setting to use split_common. (Change helix:fraanrosi keymap to use split_common #16533)
    • Switch the 'five_rows_jis' keymap setting to use split_common. (Change helix:five_rows_jis keymap to use split_common #16538)
    • Switch the 'yshrsmz' keymap setting to use split_common. (Change helix:yshrsmz keymap to use split_common #16537)
    • Switch the 'froggy' keymap setting to use split_common. (Change helix:froggy keymap to use split_common #16703)
    • Switch the 'froggy_106' keymap setting to use split_common. (Change helix:froggy_106 keymap to use split_common #16704)
  • Step2 (Helix/rev2 move to split common #16723)
    • Switch the Helix default setting to use split_common.
    • Finally, remove the previous implementation.

[mtei]

All done. Thank you!