Remove trailing whitespace (#1955)

Prevent future; "remove trailing whitespace" PR, but adding a simple
presubmit that checks for this.

This presubmit flagged quite some offenders, remove all trailing
whitespace from. Apart from that there aren't any other changes.

Signed-off-by: Miek Gieben <miek@miek.nl>

.presubmit/trailing-whitespace

@@ -0,0 +1,7 @@
+#!/bin/bash
+
+echo "** presubmit/$(basename $0)"
+
+if grep -r '[[:blank:]]$' "$@"; then
+    echo "** presubmit/$(basename $0): please remove any trailing white space"
+fi