fix: remove unneeded unconditional recipes

Commit 9c3499adf91 introduced the unconditional inclusion of the recipes
isar-exclude-docs and isar-disable-apt-cache, but they would only needed
for container images.

That would have been anyway an optimization with questionable demand,
therefore removing it.

Signed-off-by: Silvano Cirujano Cuesta <silvano.cirujano-cuesta@siemens.com>

meta/classes/image-container-extension.bbclass

@@ -6,7 +6,6 @@
 # This class extends the image.bbclass for containerizing the root filesystem.
 
 CONTAINER_FORMATS ?= "docker-archive"
-IMAGE_INSTALL += "isar-exclude-docs isar-disable-apt-cache"
 
 containerize_rootfs() {
     local cmd="/bin/dash"