5261 libm should stop using synonyms.h

*** 24,35 ****
  /*
   * Copyright 2005 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  
- #pragma weak atan2pi = __atan2pi
- 
  /*
   * atan2pi(x) = atan2(x)/pi
   */
  
  #include "libm.h"
--- 24,33 ----