Remove unreleased header for 5.8.x change log file

A new section should be added for a new 5.8 release.

[ci skip]

Signed-off-by: Maurício Meneghini Fauth <[email protected]>

Author: MauricioFauth

CHANGELOG.md

@@ -1,7 +1,5 @@
 # Change Log
 
-## [5.8.x] - YYYY-MM-DD
-
 ## [5.8.1] - 2023-09-15
 
 - Fix `:=` was not recognized as an operator just like `=` (#306)