target/xtensa: don't generate extra EXCP_DEBUG on exception

target/xtensa used to generate an extra EXCP_DEBUG exception before the
first instruction executed after an interrupt or an exception is taken
to allow single-stepping that instruction in the debugger.
This is no longer needed after the following commits:
a7ba744f ("tcg/cpu-exec: precise single-stepping after an exception")
ba3c35d9 ("tcg/cpu-exec: precise single-stepping after an interrupt")
Drop exception state tracking/extra EXCP_DEBUG generation code.

Cc: qemu-stable@nongnu.org # v5.1, v5.2, v6.0
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>