configure: don't check for the existence of iswspace() anymore

The iswspace() was only used when iswblank() was missing.  The latter
is now provided by gnulib, so it is always available, so iswspace()
is not used at all anymore.

configure.ac

@@ -470,7 +470,7 @@ int main(void)
 dnl Checks for functions.
 
 if test "x$enable_utf8" != xno; then
-    AC_CHECK_FUNCS(iswalnum iswpunct iswspace mblen mbstowcs mbtowc wctomb)
+    AC_CHECK_FUNCS(iswalnum iswpunct mblen mbstowcs mbtowc wctomb)
 fi
 dnl Checks for typedefs, structures, and compiler characteristics.
 
@@ -564,7 +564,6 @@ if test "x$enable_utf8" != xno && \
     test x$CURSES_LIB_WIDE = xyes && \
     test x$ac_cv_func_iswalnum = xyes && \
     test x$ac_cv_func_iswpunct = xyes && \
-    (test x$ac_cv_func_iswblank = xyes || test x$ac_cv_func_iswspace = xyes) && \
     test x$ac_cv_func_mblen = xyes && \
     test x$ac_cv_func_mbstowcs = xyes && \
     test x$ac_cv_func_mbtowc = xyes && \