configure: remove dead int128 test

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -2463,24 +2463,6 @@ else # "$safe_stack" = ""
 fi
 fi
 
-########################################
-# check if __[u]int128_t is usable.
-
-int128=no
-cat > $TMPC << EOF
-__int128_t a;
-__uint128_t b;
-int main (void) {
-  a = a + b;
-  b = a * b;
-  a = a * a;
-  return 0;
-}
-EOF
-if compile_prog "" "" ; then
-    int128=yes
-fi
-
 ########################################
 # check if ccache is interfering with
 # semantic analysis of macros