Updated CHANGES.txt and PHP changelog for 3.15.4 release

CHANGES.txt

@@ -1,3 +1,15 @@
+2021-03-02 version 3.15.4 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
+
+  Ruby
+  * Fixed SEGV when users pass nil messages (#8363)
+  * Fixed quadratic memory usage when appending to arrays (#8364)
+
+  C++
+  * Create a CMake option to control whether or not RTTI is enabled (#8361)
+
+  PHP
+  * read_property() handler is not supposed to return NULL (#8362)
+
 2021-02-25 version 3.15.3 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
 
   Ruby

php/ext/google/protobuf/package.xml

@@ -22,15 +22,8 @@
  </stability>
  <license uri="https://opensource.org/licenses/BSD-3-Clause">3-Clause BSD License</license>
  <notes>
- New changes in 3.15.0:
-  * unregister INI entries and fix invalid read on shutdown (#8042)
-  * Fix PhpDoc comments for message accessors to include &quot;|null&quot;. (#8136)
-  * fix: convert native PHP floats to single precision (#8187)
-  * Fixed PHP to support field numbers &gt;=2**28. (#8235)
-  * feat: add support for deprecated fields to PHP compiler (#8223)
-  * Protect against stack overflow if the user derives from Message. (#8248)
-  * Fixed clone for Message, RepeatedField, and MapField. (#8245)
-  * Updated upb to allow nonzero offset minutes in JSON timestamps. (#8258)
+ New changes in 3.15.4:
+ * read_property() handler is not supposed to return NULL (#8362)
  </notes>
  <contents>
   <dir baseinstalldir="/" name="/">