tracing: remove transform.py

This file, and a couple of uses, got left behind when the
tcg stuff was removed from tracetool.

Fixes: 126d4123 ("tracing: excise the tcg related from tracetool")
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>