[Keyboard] Refactor budget96 to remove custom i2c code in favor of QMK i2c_master (#5571)

* remove custom i2c code in favor of QMK i2c_master

* fix readme

* disable bootmagic as it doesn't work on bmc boards

keyboards/donutcables/budget96/rules.mk

@@ -31,7 +31,7 @@ F_CPU = 12000000
 BOOTLOADER = bootloadHID
 
 # build options
-BOOTMAGIC_ENABLE = lite
+BOOTMAGIC_ENABLE = no
 MOUSEKEY_ENABLE = yes
 EXTRAKEY_ENABLE = yes
 CONSOLE_ENABLE = yes
@@ -43,7 +43,7 @@ RGBLIGHT_CUSTOM_DRIVER = yes
 OPT_DEFS = -DDEBUG_LEVEL=0
 
 # custom matrix setup
-SRC = i2c.c
+SRC = i2c_master.c
 
 # programming options
 PROGRAM_CMD = ./util/atmega32a_program.py $(TARGET).hex