Fix compilation error for GH60 satan HHKB 7u layout

[aming]

Fix compilation error for GH60 satan HHKB 7u layout

Description

The HHKB 7u layout for GH60 satan failed the compilation. It maybe caused by merging multiple GH60 layouts into the same directory.

• Add the missing LAYOUT_60_hhkb layout
• Remove #define ______ KC_TRNS in keymap.c and use the definition from upstream.

Tested by on GH60 satan keyboard and compilation result as follow:

❯ qmk compile -kb gh60/satan -km hhkb_7u
Ψ Compiling keymap with gmake --jobs=1 gh60/satan:hhkb_7u


QMK Firmware 0.6.49
⚠ gh60/satan: RGBLIGHT_ANIMATIONS in config.h is deprecated and will be removed at a later date
Making gh60/satan with keymap hhkb_7u

⚠ gh60/satan: RGBLIGHT_ANIMATIONS in config.h is deprecated and will be removed at a later date
avr-gcc (Homebrew AVR GCC 8.5.0) 8.5.0
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Size before:
   text	   data	    bss	    dec	    hex	filename
      0	  26056	      0	  26056	   65c8	gh60_satan_hhkb_7u.hex

Compiling: quantum/keymap_introspection.c                                                           [OK]
Compiling: quantum/command.c                                                                        [OK]
Linking: .build/gh60_satan_hhkb_7u.elf                                                              [OK]
Creating load file for flashing: .build/gh60_satan_hhkb_7u.hex                                      [OK]
Copying gh60_satan_hhkb_7u.hex to qmk_firmware folder                                               [OK]
Checking file size of gh60_satan_hhkb_7u.hex                                                        [OK]
 * The firmware size is fine - 26056/28672 (90%, 2616 bytes free)

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

• [Bug] Compilation failed for GH60 satan with HHKB 7u keymap #18251

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).