scripts/coccinelle: New script to remove unnecessary timer_del() calls

Now that timer_free() implicitly calls timer_del(), sequences
  timer_del(mytimer);
  timer_free(mytimer);

can be simplified to just
  timer_free(mytimer);

Add a Coccinelle script to do this transformation.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20201215154107.3255-3-peter.maydell@linaro.org

scripts/coccinelle/timer-del-timer-free.cocci

+// Remove superfluous timer_del() calls
+//
+// Copyright Linaro Limited 2020
+// This work is licensed under the terms of the GNU GPLv2 or later.
+//
+// spatch --macro-file scripts/cocci-macro-file.h \
+//        --sp-file scripts/coccinelle/timer-del-timer-free.cocci \
+//        --in-place --dir .
+//
+// The timer_free() function now implicitly calls timer_del()
+// for you, so calls to timer_del() immediately before the
+// timer_free() of the same timer can be deleted.
+
+@@
+expression T;
+@@
+-timer_del(T);
+ timer_free(T);