Use QMK_KEYBOARD_H instead of the mykeyboard.h (#2780)

quantum/template/keymaps/default/keymap.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 "%KEYBOARD%.h"
+#include QMK_KEYBOARD_H
 
 const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
 [0] = LAYOUT( /* Base */