Made Serial and I2C not include the Other

This saves 192 bytes

keyboards/lets_split/config.h

@@ -41,6 +41,11 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 // #define USE_I2C
 
+// Use serial if not using I2C
+#ifndef USE_I2C
+#  define USE_SERIAL
+#endif
+
 // #define EE_HANDS
 
 #define I2C_MASTER_LEFT
@@ -94,4 +99,4 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 //#define NO_ACTION_MACRO
 //#define NO_ACTION_FUNCTION
 
-#endif
+#endif