Change 'helix/rev2:default' setting to use split_common

[mtei]

Description

Changed the following Helix keymaps to use split_common.

• default
• five_rows
• led_test

The following Helix keymaps isn't ready to use split_common, so use the same local custom implementation as before.
In this PR, there is no change in the binary of the build result of the following keymap.

• edvorakjp
• five_rows_jis
• fraanrosi
• yshrsmz
• froggy
• froggy_106

@MakotoKurauchi, This PR needs your review and approval.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

• Change the Helix keyboard to use split_common. #16388

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[zvecr]

Modifying user keymaps on master needs user sign off (strictly speaking this should have also happened on 16418). Compiling to the same binary is not enough to skip this, as its the change to the files that is the issue.

[mtei]

For the keymaps 'five_rows_jis', 'fraanrosi', 'yshrsmz', 'froggy' and 'froggy_106'

• 'keymap.c'
  I have not made any changes.
• 'rules.mk'
  Added a setting to cancel changes to default settings made in 'helix/rev2/rules.mk'.
  This was done so as not to change the build result.

[zvecr]

Not the point. User files include rules.mk and have been modified by a third party.

https://docs.qmk.fm/#/contributing?id=general-guidelines

IMPORTANT: If you would like to contribute a bugfix or improvement to user code, such as non-default keymaps, userspace and layouts, be sure to tag the original submitter of the code in your PR. Many users, regardless of skill level with Git and GitHub, may be confused or frustrated at their code being modified without their knowledge.

Again, the fact the build result hasnt changed, isnt enough to skip notifying users.

[mtei]

OKey.
Canceled all keymap changes except for default and my five_rows, led_test.