cmdlib: don't use cache qcow for composes; use virtiofs

Now that our OSBuild workflow is using the cache we saw at least one
case where the pipeline was running out of space when composing the
extensions. Since we had a previous proposal [1] to just drop the
cache altogether anyway let's try to at least remove it from the
runcompose functions to eliminate the use of it there anyway.

[1] #3615

src/cmdlib.sh

@@ -563,7 +563,7 @@ runcompose_tree() {
         (umask 0022 && sudo -E "$@")
         sudo chown -R -h "${USER}":"${USER}" "${tmprepo}"
     else
-        runvm_with_cache -- "$@" --repo "${repo}" --write-composejson-to "${composejson}"
+        runvm -- "$@" --repo "${repo}" --write-composejson-to "${composejson}"
     fi
 }
 
@@ -587,7 +587,7 @@ runcompose_extensions() {
         (umask 0022 && sudo -E "$@")
         sudo chown -R -h "${USER}":"${USER}" "${outputdir}"
     else
-        runvm_with_cache -- "$@"
+        runvm -- "$@"
     fi
 }