Fix acceptance tests to actually verify config-based engine resolution

Change DATABRICKS_BUNDLE_ENGINE from ["direct"] to [] in bind/unbind
engine-from-config tests. With ["direct"], env and config agreed so a
regression back to engine.FromEnv() would still pass. With [], the env
var is unset and the tests verify that bind/unbind read engine from
bundle.engine config.

Task-review: /Users/denis.bilenko/work/prompts/features/bundle-engine-vs-env/003.SUMMARY.md

Co-authored-by: Isaac

Author: denik

acceptance/bundle/deployment/bind/job/engine-from-config/out.test.toml

@@ -1,6 +1,6 @@
 Cloud = false # test leaves deployed job
 Ignore = [".databricks"]
 
-# Use ["direct"] to verify bind respects bundle.engine config (not just env var).
+# Omit DATABRICKS_BUNDLE_ENGINE so bind must read engine from bundle.engine config.
 [EnvMatrix]
-  DATABRICKS_BUNDLE_ENGINE = ["direct"]
+  DATABRICKS_BUNDLE_ENGINE = []

acceptance/bundle/deployment/bind/job/engine-from-config/test.toml

@@ -1,6 +1,6 @@
 Cloud = false # test leaves deployed job
 Ignore = [".databricks"]
 
-# Use ["direct"] to verify unbind respects bundle.engine config (not just env var).
+# Omit DATABRICKS_BUNDLE_ENGINE so unbind must read engine from bundle.engine config.
 [EnvMatrix]
-  DATABRICKS_BUNDLE_ENGINE = ["direct"]
+  DATABRICKS_BUNDLE_ENGINE = []