test/api.sh: Drop distro aliases and dot-notation

This reverts commit 2fe5e01d4d with the
exception of the changes in tools/provision.sh.
This functionality is covered by unit tests in osbuild/images:
aaa53adc3c/pkg/distrofactory/distrofactory_test.go (L9)

test/cases/api/container.registry.sh

@@ -42,7 +42,7 @@ EOF
 function createReqFile() {
       cat > "$REQUEST_FILE" << EOF
 {
-  "distribution": "$DISTRO_NAME",
+  "distribution": "$DISTRO",
   "customizations": {
     "payload_repositories": [
       {