Revert "Updated UPGRADING for ext/ereg removal"

This reverts commit 610ef5d.

Author: dstogov

UPGRADING

@@ -71,20 +71,11 @@ PHP X.Y UPGRADE NOTES
 8. Removed Extensions
 ========================================
 
-- ereg
 
 ========================================
 9. Other Changes to Extensions
 ========================================
 
-- mbstring
-  . Removed constant 'MB_OVERLOAD_REGEX'
-
-- opcache
-  . Now uses PCRE for blacklist filtering
-
-- pgsql
-  . Now uses PCRE for column type detection
 
 ========================================
 10. New Global Constants