[ci skip] Fix NEWS entries

These entries are duplicates, but also shouldn't be here in the first
place because they were also merged into stable branches.

Author: ndossche

NEWS

@@ -23,10 +23,6 @@ PHP                                                                        NEWS
   . Fixed bug GH-20426 (Spoofchecker::setRestrictionLevel() error message
     suggests missing constants). (DanielEScherzer)
 
-- Mbstring
-  . Fixed bug GH-20674 (Fix GH-20674 mb_decode_mimeheader does not handle
-    separator). (Yuya Hamada)
-
 - Fibers:
   . Fixed bug GH-20483 (ASAN stack overflow with fiber.stack_size INI
     small value). (David Carlier)
@@ -35,8 +31,6 @@ PHP                                                                        NEWS
   . ini_set() with mbstring.detect_order changes the order of mb_detect_order
     as intended, since mbstring.detect_order is an INI_ALL setting. (tobee94)
   . Added GB18030-2022 to default encoding list for zh-CN. (HeRaNO)
-  . Fixed bug GH-20674 (Fix GH-20674 mb_decode_mimeheader does not handle
-    separator). (Yuya Hamada)
 
 - Opcache:
   . Fixed bug GH-20051 (apache2 shutdowns when restart is requested during