Remove 8.7 release highlights link to fix docs build (#93604)

docs/reference/migration/migrate_8_8.asciidoc

@@ -7,7 +7,7 @@
 This section discusses the changes that you need to be aware of when migrating
 your application to {es} 8.8.
 
-See also {ref-bare}/8.8/release-highlights.html[What's new in 8.8] and <<es-release-notes>>.
+See also <<release-highlights>> and <<es-release-notes>>.
 
 coming::[8.8.0]
 

docs/reference/release-notes/highlights.asciidoc

@@ -12,8 +12,7 @@ endif::[]
 // Add previous release to the list
 Other versions:
 
-{ref-bare}/8.7/release-highlights.html[8.7]
-| {ref-bare}/8.6/release-highlights.html[8.6]
+{ref-bare}/8.6/release-highlights.html[8.6]
 | {ref-bare}/8.5/release-highlights.html[8.5]
 | {ref-bare}/8.4/release-highlights.html[8.4]
 | {ref-bare}/8.3/release-highlights.html[8.3]