[Keyboard] Pearl Refactors (#5907)

* use pragma once

* remove custom matrix

* remove custom i2c code in favor of QMK's i2c_master

* rename to all lower case readme

* update readme

* turn off bootmagic as it doesn't work anyway

* Update keyboards/pearl/readme.md

Co-Authored-By: noroadsleft <18669334+noroadsleft@users.noreply.github.com>

keyboards/pearl/rules.mk

@@ -31,7 +31,7 @@ F_CPU = 12000000
 BOOTLOADER = bootloadHID
 
 # build options
-BOOTMAGIC_ENABLE = full
+BOOTMAGIC_ENABLE = no
 MOUSEKEY_ENABLE = no
 EXTRAKEY_ENABLE = yes
 CONSOLE_ENABLE = yes
@@ -43,8 +43,7 @@ RGBLIGHT_CUSTOM_DRIVER = yes
 OPT_DEFS = -DDEBUG_LEVEL=0
 
 # custom matrix setup
-CUSTOM_MATRIX = yes
-SRC = matrix.c i2c.c
+SRC = i2c_master.c
 
 # programming options
 PROGRAM_CMD = ./util/atmega32a_program.py $(TARGET).hex