Fix Circuitplay core and tools reference

While not plainly wrong, since the board is not contained in a 3rd party package, use the "baseline" reference method

Author: facchinm

hardware/arduino/avr/boards.txt

@@ -887,12 +887,12 @@ circuitplay32u4cat.bootloader.extended_fuses=0xcb
 circuitplay32u4cat.bootloader.file=caterina/Caterina-Circuitplay32u4.hex
 circuitplay32u4cat.bootloader.unlock_bits=0x3F
 circuitplay32u4cat.bootloader.lock_bits=0x2F
-circuitplay32u4cat.bootloader.tool=arduino:avrdude
+circuitplay32u4cat.bootloader.tool=avrdude
 circuitplay32u4cat.build.mcu=atmega32u4
 circuitplay32u4cat.build.f_cpu=8000000L
 circuitplay32u4cat.build.vid=0x239A
 circuitplay32u4cat.build.pid=0x8011
-circuitplay32u4cat.build.core=arduino:arduino
+circuitplay32u4cat.build.core=arduino
 circuitplay32u4cat.build.variant=circuitplay32u4
 circuitplay32u4cat.build.board=AVR_CIRCUITPLAY
 circuitplay32u4cat.build.usb_product="Circuit Playground"