ktest.pl: Remove unused declarations in run_bisect_test function

Since $output and $ret are not used in the subsequent code, the declarations
should be removed.

Fixes: a75fecec ("ktest: Added sample.conf, new %default option format")
Link: https://lore.kernel.org/20240902130735.6034-1-bajing@cmss.chinamobile.com


Signed-off-by: Ba Jing <bajing@cmss.chinamobile.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>