Remove Facebook CLA check from merge rules (pytorch#23132)

Summary:
- Remove Facebook CLA Check from the mandatory merge checks.
- Keep the existing Lint and pull requirements unchanged.

Test plan:
- Parsed .github/merge_rules.yaml with PyYAML.
- Ran git diff --check.

Authored with OpenAI Codex.

Author: JakeStevens

.github/merge_rules.yaml

@@ -4,6 +4,6 @@
   approved_by:
   - pytorch/metamates
   mandatory_checks_name:
-  - Facebook CLA Check
+  - EasyCLA
   - Lint
   - pull