Remove deprecated 'forbid_global_implied_dsr' feature flag

'forbid_global_implied_dsr' feature flag was added for Mitaka
and older branches which are not supported now.

Devstack already removed this feature flag setting
- Ia1eb87d68a6265d8541cb87a88523246885e5a8a

This commit removes this from tempest.

Change-Id: I5422e33867a6038e8a4782dbdc639434a3c2b4b6
diff --git a/releasenotes/notes/removal-deprecated-config-options-3db535b979fe3509.yaml b/releasenotes/notes/removal-deprecated-config-options-3db535b979fe3509.yaml
new file mode 100644
index 0000000..dbb6c46
--- /dev/null
+++ b/releasenotes/notes/removal-deprecated-config-options-3db535b979fe3509.yaml
@@ -0,0 +1,8 @@
+---
+upgrade:
+  - |
+    Below config options or feature flags were deprecated for removal.
+    It's time to remove them as all supported stable branches are
+    good to handle them.
+
+    * ``[identity-feature-enabled].forbid_global_implied_dsr``