remove unused (redundant) chapter names

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66333 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

NEWS

@@ -537,8 +537,6 @@ sufficient information, see the ChangeLog file or Redmine
 
 === C API updates
 
-=== Supported platform changes
-
 === Implementation improvements
 
 * Speedup Proc#call because we don't need to care about <code>$SAFE</code>
@@ -592,6 +590,4 @@ sufficient information, see the ChangeLog file or Redmine
     * libruby.2.6.dylib
     * libruby.dylib -> libruby.2.6.dylib
 
-=== Misc
-
 * Extracted misc/*.el files to https://github.com/ruby/elisp