ftrace: Fix direct_functions leak in update_ftrace_direct_del

ftrace: Fix direct_functions leak in update_ftrace_direct_del

Alexei reported memory leak in update_ftrace_direct_del.
We miss cleanup of the replaced direct_functions in the
success path in update_ftrace_direct_del, adding that.

Fixes: 8d2c1233f371 ("ftrace: Add update_ftrace_direct_del function")
Reported-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Closes: https://lore.kernel.org/bpf/aX_BxG5EJTJdCMT9@krava/T/#m7c13f5a95f862ed7ab78e905fbb678d635306a0c
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20260202075849.1684369-1-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>