Remove useless "ifdef KEYBOARD_*" (#20078)

Co-authored-by: Nick Brassel <[email protected]>

keyboards/handwired/split65/split65.c

@@ -13,7 +13,7 @@
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
-#include "split65.h"
+#include "quantum.h"
 
 // OLED Code inspired by https://github.com/qmk/qmk_firmware/blob/master/keyboards/splitkb/kyria/rev1/rev1.c