Change keyboard level include guards to pragma once (#14248)

* Change keyboard level include guards to `pragma once`

And clean up a lot of layout macros

* Oops

* Remove dangling endif

keyboards/dc01/left/i2c.h

@@ -1,5 +1,4 @@
-#ifndef I2C_H
-#define I2C_H
+#pragma once
 
 #include <stdint.h>
 
@@ -27,5 +26,3 @@ uint8_t i2c_master_write(uint8_t data);
 uint8_t i2c_master_read(int);
 void i2c_reset_state(void);
 void i2c_slave_init(uint8_t address);
-
-#endif