feat: remove staging layer in container build

This PR removes the staging layer.

.gitlab-ci.yml

@@ -449,7 +449,7 @@ eic:
                    2>&1 | tee build.log
       ; do
         if grep "unknown blob" build.log ; then
-          BUILD_OPTIONS="--no-cache-filter spack,builder,staging,runtime ${BUILD_OPTIONS}" ;
+          BUILD_OPTIONS="--no-cache-filter spack,builder,runtime ${BUILD_OPTIONS}" ;
         else
           exit 1 ;
         fi ;