tests/setup: Remove use of libtool's --debug option.

[Jim Meyering]

I used this --debug option a few weeks ago.
It's no longer needed.

        * tests/setup: Remove use of libtool's --debug option.

Index: tests/setup
===================================================================
--- tests/setup (revision 506983)
+++ tests/setup (working copy)
@@ -30,7 +30,7 @@
 if test x$VALGRIND = x; then
   vg=
 else
-  vg="libtool --debug --mode=execute valgrind `echo $vg_options` --"
+  vg="libtool --mode=execute valgrind `echo $vg_options` --"
 fi

 vg_leak_check()