selftests: timers: remove rtctest_setdate from run_destructive_tests

Remove rtctest_setdate from run_destructive_tests target. Leave it in
TEST_GEN_PROGS_EXTENDED to be included in the install targets.

Suggested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
Reviewed-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>