Remove unused image-cache CRD
Remove unused image-cache CRD

The image-cache CRD is a legacy from the knative days of Tekton.
It is not used by Tekton today, so it should be removed now.

Signed-off-by: Andrea Frittoli <4cec69a2e3f23b658ef5550bf7c5b5012f9473f7@uk.ibm.com>

tektoncd/pipeline,tektoncd/pipeline