update release notes pages/sections in docu

Author: svigerske

CHANGELOG

@@ -1,4 +1,4 @@
-@page RN90 Release notes for SCIP 9
+@page RN9 Release notes for SCIP 9
 
 @section RN910 SCIP 9.1.0
 *************************
@@ -406,7 +406,7 @@ Miscellaneous
   (scip/type_retcode.h, scip/type_message.h, scip/pub_message.h)
 
 
-@page RN81 Release notes for SCIP 8.1
+@page RN8 Release notes for SCIP 8
 
 @section RN810 SCIP 8.1.0
 *************************
@@ -481,8 +481,6 @@ Miscellaneous
 
 - the parameter change callback is no longer called at the moment a parameter is created
 
-@page RN80 Release notes for SCIP 8.0
-
 @section RN804 SCIP 8.0.4
 *************************
 

doc/xternal.c

@@ -405,8 +405,8 @@
  * New features, peformance improvements, and interface changes between different versions of SCIP are documented in the
  * release notes:
  *
- * - \subpage RN81         "SCIP 8.1"
- * - \subpage RN80         "SCIP 8.0"
+ * - \subpage RN9          "SCIP 9"
+ * - \subpage RN8          "SCIP 8"
  * - \subpage RN70         "SCIP 7.0"
  * - \subpage RN60         "SCIP 6.0"
  * - \subpage RN50         "SCIP 5.0"