[DOCS] Remove unused file (#58208)

docs/reference/release-notes/highlights-8.0.0.asciidoc

@@ -1,16 +0,0 @@
-[[release-highlights-8.0.0]]
-== 8.0.0 release highlights
-++++
-<titleabbrev>8.0.0</titleabbrev>
-++++
-
-coming[8.0.0]
-
-See also <<breaking-changes-8.0,Breaking changes>> and <<release-notes-8.0.0-alpha1,Release notes>>.
-
-//NOTE: The notable-highlights tagged regions are re-used in the
-//Installation and Upgrade Guide
-
-// tag::notable-highlights[]
-
-// end::notable-highlights[]