Revert eachSupportedId guard — env var fix is sufficient

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Fredrik Adelöw <freben@gmail.com>

.changeset/fix-empty-each-tests.md

@@ -1,5 +0,0 @@
----
-'@backstage/backend-test-utils': patch
----
-
-Fixed a crash in test suites that use `TestDatabases` or `TestCaches` when none of the requested database or cache engines are available. Previously, `eachSupportedId()` would return an empty array causing `describe.each` to throw and prevent the entire suite from running. Now returns a placeholder entry so individual tests report a clear failure instead.

packages/backend-test-utils/src/cache/TestCaches.ts

@@ -108,9 +108,6 @@ export class TestCaches {
   }
 
   eachSupportedId(): [TestCacheId][] {
-    if (this.supportedIds.length === 0) {
-      return [['MISSING' as TestCacheId]];
-    }
     return this.supportedIds.map(id => [id]);
   }
 

packages/backend-test-utils/src/database/TestDatabases.ts

@@ -124,13 +124,6 @@ export class TestDatabases {
   }
 
   eachSupportedId(): [TestDatabaseId][] {
-    if (this.supportedIds.length === 0) {
-      // Return a placeholder so that describe.each/it.each does not throw
-      // when no databases are available. The init() call will throw for
-      // the unknown ID, causing the test to be reported as failed rather
-      // than crashing the entire suite.
-      return [['MISSING' as TestDatabaseId]];
-    }
     return this.supportedIds.map(id => [id]);
   }