make: Remove unused IMAGES from image Makefiles

Many of the `rook/images/<image>/` directory Makefiles defined a
variable called `IMAGES`, which was unused and causing some developer
confusion with the feature adding the ability to specify which backend
images to build. Remove these unused instances.

Signed-off-by: Blaine Gardner <blaine.gardner@suse.com>

images/ceph-toolbox/Makefile

@@ -16,7 +16,6 @@ include ../image.mk
 
 TOOLBOX_IMAGE = $(BUILD_REGISTRY)/ceph-toolbox-$(GOARCH)
 TOOLBOX_BASE_IMAGE = $(BUILD_REGISTRY)/ceph-toolbox-base-$(GOARCH)
-IMAGES = $(TOOLBOX_IMAGE) $(TOOLBOX_BASE_IMAGE)
 CACHE_IMAGES = $(TOOLBOX_BASE_IMAGE)
 
 CEPH_VERSION = $(shell cat ../ceph/ceph_version)

images/ceph/Makefile

@@ -18,7 +18,6 @@ include ../image.mk
 # Image Build Options
 
 CEPH_IMAGE = $(BUILD_REGISTRY)/ceph-$(GOARCH)
-IMAGES = $(CEPH_IMAGE)
 
 CEPH_VERSION = $(shell cat ceph_version)
 BASEIMAGE = $(CEPH_VERSION)-$(PLATFORM_ARCH)

images/cockroachdb/Makefile

@@ -18,7 +18,6 @@ include ../image.mk
 # Image Build Options
 
 COCKROACHDB_IMAGE = $(BUILD_REGISTRY)/cockroachdb-$(GOARCH)
-IMAGES = $(COCKROACHDB_IMAGE)
 
 TEMP := $(shell mktemp -d)
 

images/cross/Makefile

@@ -15,8 +15,7 @@
 include ../image.mk
 
 IMAGE = $(BUILD_REGISTRY)/cross-$(GOARCH)
-IMAGES := $(IMAGE)
-CACHE_IMAGES = $(IMAGES)
+CACHE_IMAGES = $(IMAGE)
 
 TEMP := $(shell mktemp -d)