Remove optional getrusage() declaration

Declaration provided by Newlib since 2014.

Update #3409.

cpukit/configure.ac

@@ -160,9 +160,6 @@ AC_MSG_RESULT([no])
 ])
 AC_LANG_POP(C)
 
-# Mandated by POSIX, not declared in some versions of newlib.
-AC_CHECK_DECLS([getrusage],,,[#include sys/resource.h])
-
 # Newlib's unix/ directory
 AC_CHECK_FUNCS([getcwd])
 # </FIXME>

cpukit/libcsupport/src/getrusage.c

@@ -17,10 +17,6 @@
 #include <rtems.h>
 #include <rtems/seterr.h>
 
-#if !HAVE_DECL_GETRUSAGE
-extern int getrusage(int who, struct rusage *usage);
-#endif
-
 int getrusage(int who, struct rusage *usage)
 {
   struct timespec uptime;