All the STEXI/ETEXI blocks and the Makfile rules that use them have now
been removed from the codebase. We can remove the code from the hxtool
script which handles the STEXI/ETEXI directives and the '-t' option.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200306171749.10756-4-peter.maydell@linaro.org