Remove check for EH define (#7525)

Its use in lets_split_eh was factored out in https://github.com/qmk/qmk_firmware/pull/6411

keyboards/ai03/orbit/split_util.c

@@ -54,7 +54,7 @@ bool is_keyboard_master(void)
 }
 
 static void keyboard_master_setup(void) {
-#if defined(USE_I2C) || defined(EH)
+#if defined(USE_I2C)
   #ifdef SSD1306OLED
     matrix_master_OLED_init ();
   #endif

keyboards/ai03/orbit/transport.c

@@ -18,7 +18,7 @@
   extern backlight_config_t backlight_config;
 #endif
 
-#if defined(USE_I2C) || defined(EH)
+#if defined(USE_I2C)
 
 #include "i2c.h"
 

quantum/split_common/post_config.h

@@ -1,4 +1,4 @@
-#if defined(USE_I2C) || defined(EH)
+#if defined(USE_I2C)
 // When using I2C, using rgblight implicitly involves split support.
 #    if defined(RGBLIGHT_ENABLE) && !defined(RGBLIGHT_SPLIT)
 #        define RGBLIGHT_SPLIT

quantum/split_common/split_util.c

@@ -76,7 +76,7 @@ __attribute__((weak)) bool is_keyboard_master(void) {
 }
 
 static void keyboard_master_setup(void) {
-#if defined(USE_I2C) || defined(EH)
+#if defined(USE_I2C)
 #    ifdef SSD1306OLED
     matrix_master_OLED_init();
 #    endif

quantum/split_common/transport.c

@@ -21,7 +21,7 @@ static pin_t encoders_pad[] = ENCODERS_PAD_A;
 #    define NUMBER_OF_ENCODERS (sizeof(encoders_pad) / sizeof(pin_t))
 #endif
 
-#if defined(USE_I2C) || defined(EH)
+#if defined(USE_I2C)
 
 #    include "i2c_master.h"
 #    include "i2c_slave.h"