Address review feedback: make display_name replace title

This commit addresses @codeboten's review feedback on PR open-telemetry#14115.
The display_name field now properly replaces the title in generated
README files instead of creating duplicate headings.

Changes:
- Update test metadata.yaml files with appropriate display_name values
- Clean up README files to remove duplicate titles
- Regenerate README files with display_name as the sole H1 heading

The README structure is now:
  - Description text
  - <!-- status autogenerated section -->
  - # Component Display Name (from display_name field)
  - Status table
  - <!-- end autogenerated section -->

Fixes the issue where multiple H1 headings appeared when display_name
was set, which was confusing and not the intended behavior.

Co-authored-by: SteveYi <[email protected]>

Author: thc1006

cmd/mdatagen/generated_package_test.go

@@ -1,9 +1,7 @@
-# Sample Receiver
 This receiver is used for testing purposes to check the output of mdatagen.
 
-# Sample
-
 <!-- status autogenerated section -->
+# Sample Factory Receiver
 | Status        |           |
 | ------------- |-----------|
 | Stability     | [deprecated]: profiles   |