splitkb/kyria - Resolve CONVERT_TO_PROTON_C warnings (#17617)

keyboards/splitkb/kyria/rev1/proton_c/rules.mk

@@ -9,4 +9,4 @@ WS2812_DRIVER = pwm
 SERIAL_DRIVER = usart
 AUDIO_ENABLE = no
 LTO_ENABLE = no
-CONVERT_TO_PROTON_C = yes
+CONVERT_TO = proton_c

keyboards/splitkb/kyria/rev2/proton_c/rules.mk

@@ -9,4 +9,4 @@ WS2812_DRIVER = pwm
 SERIAL_DRIVER = usart
 AUDIO_ENABLE = no
 LTO_ENABLE = no
-CONVERT_TO_PROTON_C = yes
+CONVERT_TO = proton_c