Remove make all-<platform> build targets (#19496)

builddefs/build_keyboard.mk

@@ -433,13 +433,6 @@ SRC += $(TMK_COMMON_SRC)
 OPT_DEFS += $(TMK_COMMON_DEFS)
 EXTRALDFLAGS += $(TMK_COMMON_LDFLAGS)
 
-SKIP_COMPILE := no
-ifneq ($(REQUIRE_PLATFORM_KEY),)
-    ifneq ($(REQUIRE_PLATFORM_KEY),$(PLATFORM_KEY))
-        SKIP_COMPILE := yes
-    endif
-endif
-
 -include $(PLATFORM_PATH)/$(PLATFORM_KEY)/bootloader.mk
 include $(PLATFORM_PATH)/$(PLATFORM_KEY)/platform.mk
 -include $(PLATFORM_PATH)/$(PLATFORM_KEY)/flash.mk
@@ -479,12 +472,7 @@ $(KEYBOARD_OUTPUT)_INC := $(PROJECT_INC)
 $(KEYBOARD_OUTPUT)_CONFIG := $(PROJECT_CONFIG)
 
 # Default target.
-ifeq ($(SKIP_COMPILE),no)
 all: build check-size
-else
-all:
-	echo "skipped" >&2
-endif
 
 build: elf cpfirmware
 check-size: build