Remove about ext/psych/yaml which is no longer bundled [ci skip]

LEGAL

@@ -748,8 +748,7 @@ mentioned below.
 [ext/psych]
 [test/psych]
 
-  The files under these directories are under the following license, except for
-  ext/psych/yaml.
+  The files under these directories are under the following license.
 
   >>>
     Copyright 2009:: Aaron Patterson, et al.
@@ -772,31 +771,6 @@ mentioned below.
     OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
     SOFTWARE.
 
-[ext/psych/yaml]
-
-  The files under this directory are under the following license.
-
-  >>>
-    Copyright (c) 2006:: Kirill Simonov
-
-    Permission is hereby granted, free of charge, to any person obtaining a copy of
-    this software and associated documentation files (the "Software"), to deal in
-    the Software without restriction, including without limitation the rights to
-    use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
-    of the Software, and to permit persons to whom the Software is furnished to do
-    so, subject to the following conditions:
-
-    The above copyright notice and this permission notice shall be included in all
-    copies or substantial portions of the Software.
-
-    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-    SOFTWARE.
-
 [ext/pty/pty.c]
 
   >>>